| Message ID | 20161122164106.31852-1-Liviu.Dudau@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: > drm_get_format_name() de-references the buf parameter without checking > if the pointer was not NULL. Given that the function is EXPORT-ed, lets > sanitise the parameters before proceeding. > > Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) > Cc: Eric Engestrom <eric@engestrom.ch> > Cc: Rob Clark <robdclark@gmail.com> > Cc: Jani Nikula <jani.nikula@intel.com> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > > Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> > --- > drivers/gpu/drm/drm_fourcc.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > index 90d2cc8..0a3ff0b 100644 > --- a/drivers/gpu/drm/drm_fourcc.c > +++ b/drivers/gpu/drm/drm_fourcc.c > @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); > */ > const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) > { > + if (!buf) > + return NULL; > + Seems rather pointless to me. Why would you ever pass NULL to this guy? > snprintf(buf->str, sizeof(buf->str), > "%c%c%c%c %s-endian (0x%08x)", > printable_char(format & 0xff), > -- > 2.10.2 > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote: > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: >> drm_get_format_name() de-references the buf parameter without checking >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets >> sanitise the parameters before proceeding. >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) >> Cc: Eric Engestrom <eric@engestrom.ch> >> Cc: Rob Clark <robdclark@gmail.com> >> Cc: Jani Nikula <jani.nikula@intel.com> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> >> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> >> --- >> drivers/gpu/drm/drm_fourcc.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c >> index 90d2cc8..0a3ff0b 100644 >> --- a/drivers/gpu/drm/drm_fourcc.c >> +++ b/drivers/gpu/drm/drm_fourcc.c >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); >> */ >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) >> { >> + if (!buf) >> + return NULL; >> + > > Seems rather pointless to me. Why would you ever pass NULL to this guy? perhaps BUG_ON(!buf)... BR, -R >> snprintf(buf->str, sizeof(buf->str), >> "%c%c%c%c %s-endian (0x%08x)", >> printable_char(format & 0xff), >> -- >> 2.10.2 >> >> _______________________________________________ >> dri-devel mailing list >> dri-devel@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > > -- > Ville Syrjälä > Intel OTC > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: > On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä > <ville.syrjala@linux.intel.com> wrote: > > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: > >> drm_get_format_name() de-references the buf parameter without checking > >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets > >> sanitise the parameters before proceeding. > >> > >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) > >> Cc: Eric Engestrom <eric@engestrom.ch> > >> Cc: Rob Clark <robdclark@gmail.com> > >> Cc: Jani Nikula <jani.nikula@intel.com> > >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > >> > >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> > >> --- > >> drivers/gpu/drm/drm_fourcc.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > >> index 90d2cc8..0a3ff0b 100644 > >> --- a/drivers/gpu/drm/drm_fourcc.c > >> +++ b/drivers/gpu/drm/drm_fourcc.c > >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); > >> */ > >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) > >> { > >> + if (!buf) > >> + return NULL; > >> + > > > > Seems rather pointless to me. Why would you ever pass NULL to this guy? > > perhaps BUG_ON(!buf)... And how does that differ from just buf->foo? > > BR, > -R > > >> snprintf(buf->str, sizeof(buf->str), > >> "%c%c%c%c %s-endian (0x%08x)", > >> printable_char(format & 0xff), > >> -- > >> 2.10.2 > >> > >> _______________________________________________ > >> dri-devel mailing list > >> dri-devel@lists.freedesktop.org > >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- > > Ville Syrjälä > > Intel OTC > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Tue, Nov 22, 2016 at 12:31 PM, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote: > On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: >> On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä >> <ville.syrjala@linux.intel.com> wrote: >> > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: >> >> drm_get_format_name() de-references the buf parameter without checking >> >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets >> >> sanitise the parameters before proceeding. >> >> >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) >> >> Cc: Eric Engestrom <eric@engestrom.ch> >> >> Cc: Rob Clark <robdclark@gmail.com> >> >> Cc: Jani Nikula <jani.nikula@intel.com> >> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> >> >> >> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> >> >> --- >> >> drivers/gpu/drm/drm_fourcc.c | 3 +++ >> >> 1 file changed, 3 insertions(+) >> >> >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c >> >> index 90d2cc8..0a3ff0b 100644 >> >> --- a/drivers/gpu/drm/drm_fourcc.c >> >> +++ b/drivers/gpu/drm/drm_fourcc.c >> >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); >> >> */ >> >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) >> >> { >> >> + if (!buf) >> >> + return NULL; >> >> + >> > >> > Seems rather pointless to me. Why would you ever pass NULL to this guy? >> >> perhaps BUG_ON(!buf)... > > And how does that differ from just buf->foo? it gets you a file and line # in the error splat.. not that drm_get_format_name() is such a big function that it would be difficult to decipher the null deref crash, but if we added anything it should be BUG_ON() to make it clear that passing null isn't a caller error. BR, -R >> >> BR, >> -R >> >> >> snprintf(buf->str, sizeof(buf->str), >> >> "%c%c%c%c %s-endian (0x%08x)", >> >> printable_char(format & 0xff), >> >> -- >> >> 2.10.2 >> >> >> >> _______________________________________________ >> >> dri-devel mailing list >> >> dri-devel@lists.freedesktop.org >> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel >> > >> > -- >> > Ville Syrjälä >> > Intel OTC >> > _______________________________________________ >> > dri-devel mailing list >> > dri-devel@lists.freedesktop.org >> > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > -- > Ville Syrjälä > Intel OTC
On Tue, Nov 22, 2016 at 12:35:53PM -0500, Rob Clark wrote: > On Tue, Nov 22, 2016 at 12:31 PM, Ville Syrjälä > <ville.syrjala@linux.intel.com> wrote: > > On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: > >> On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä > >> <ville.syrjala@linux.intel.com> wrote: > >> > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: > >> >> drm_get_format_name() de-references the buf parameter without checking > >> >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets > >> >> sanitise the parameters before proceeding. > >> >> > >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) > >> >> Cc: Eric Engestrom <eric@engestrom.ch> > >> >> Cc: Rob Clark <robdclark@gmail.com> > >> >> Cc: Jani Nikula <jani.nikula@intel.com> > >> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > >> >> > >> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> > >> >> --- > >> >> drivers/gpu/drm/drm_fourcc.c | 3 +++ > >> >> 1 file changed, 3 insertions(+) > >> >> > >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > >> >> index 90d2cc8..0a3ff0b 100644 > >> >> --- a/drivers/gpu/drm/drm_fourcc.c > >> >> +++ b/drivers/gpu/drm/drm_fourcc.c > >> >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); > >> >> */ > >> >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) > >> >> { > >> >> + if (!buf) > >> >> + return NULL; > >> >> + > >> > > >> > Seems rather pointless to me. Why would you ever pass NULL to this guy? > >> > >> perhaps BUG_ON(!buf)... > > > > And how does that differ from just buf->foo? > > it gets you a file and line # in the error splat.. not that > drm_get_format_name() is such a big function that it would be > difficult to decipher the null deref crash, but if we added anything > it should be BUG_ON() to make it clear that passing null isn't a > caller error. Yeah, BUG_ON() at least documents the intent, so it's better than the null check. But for something like this even BUG_ON() is just wasted bytes IMO. BUG_ON() can be useful for those weird bugs where somewhere deep down you hit a null pointer and you can't figure out where the bad pointer came from. So you might sprinkle a few BUG_ONs() further up to catch it sooner. Esp. if you can't reproduce the bug yourself and have to rely on user(s) to find it for you. Even WARN_ON() w/ or w/o an early bailout might be a decent idea sometimes since it might have a slightly higher chance of keeping the kernel in working condition, but IMO just blindly throwing it around everywhere is not a good approach.
On Tue, Nov 22, 2016 at 1:06 PM, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote: > On Tue, Nov 22, 2016 at 12:35:53PM -0500, Rob Clark wrote: >> On Tue, Nov 22, 2016 at 12:31 PM, Ville Syrjälä >> <ville.syrjala@linux.intel.com> wrote: >> > On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: >> >> On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä >> >> <ville.syrjala@linux.intel.com> wrote: >> >> > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: >> >> >> drm_get_format_name() de-references the buf parameter without checking >> >> >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets >> >> >> sanitise the parameters before proceeding. >> >> >> >> >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) >> >> >> Cc: Eric Engestrom <eric@engestrom.ch> >> >> >> Cc: Rob Clark <robdclark@gmail.com> >> >> >> Cc: Jani Nikula <jani.nikula@intel.com> >> >> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> >> >> >> >> >> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> >> >> >> --- >> >> >> drivers/gpu/drm/drm_fourcc.c | 3 +++ >> >> >> 1 file changed, 3 insertions(+) >> >> >> >> >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c >> >> >> index 90d2cc8..0a3ff0b 100644 >> >> >> --- a/drivers/gpu/drm/drm_fourcc.c >> >> >> +++ b/drivers/gpu/drm/drm_fourcc.c >> >> >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); >> >> >> */ >> >> >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) >> >> >> { >> >> >> + if (!buf) >> >> >> + return NULL; >> >> >> + >> >> > >> >> > Seems rather pointless to me. Why would you ever pass NULL to this guy? >> >> >> >> perhaps BUG_ON(!buf)... >> > >> > And how does that differ from just buf->foo? >> >> it gets you a file and line # in the error splat.. not that >> drm_get_format_name() is such a big function that it would be >> difficult to decipher the null deref crash, but if we added anything >> it should be BUG_ON() to make it clear that passing null isn't a >> caller error. > > Yeah, BUG_ON() at least documents the intent, so it's better than > the null check. But for something like this even BUG_ON() is > just wasted bytes IMO. +1 The patch has a Fixes line, but AFAICT, the referenced patch didn't introduce any NULL opportunities that weren't previously there. Sean > > BUG_ON() can be useful for those weird bugs where somewhere deep > down you hit a null pointer and you can't figure out where the > bad pointer came from. So you might sprinkle a few BUG_ONs() > further up to catch it sooner. Esp. if you can't reproduce the > bug yourself and have to rely on user(s) to find it for you. > > Even WARN_ON() w/ or w/o an early bailout might be a decent idea > sometimes since it might have a slightly higher chance of keeping > the kernel in working condition, but IMO just blindly throwing > it around everywhere is not a good approach. > > -- > Ville Syrjälä > Intel OTC > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Tue, Nov 22, 2016 at 01:15:08PM -0500, Sean Paul wrote: > On Tue, Nov 22, 2016 at 1:06 PM, Ville Syrjälä > <ville.syrjala@linux.intel.com> wrote: > > On Tue, Nov 22, 2016 at 12:35:53PM -0500, Rob Clark wrote: > >> On Tue, Nov 22, 2016 at 12:31 PM, Ville Syrjälä > >> <ville.syrjala@linux.intel.com> wrote: > >> > On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: > >> >> On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä > >> >> <ville.syrjala@linux.intel.com> wrote: > >> >> > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: > >> >> >> drm_get_format_name() de-references the buf parameter without checking > >> >> >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets > >> >> >> sanitise the parameters before proceeding. > >> >> >> > >> >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) > >> >> >> Cc: Eric Engestrom <eric@engestrom.ch> > >> >> >> Cc: Rob Clark <robdclark@gmail.com> > >> >> >> Cc: Jani Nikula <jani.nikula@intel.com> > >> >> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > >> >> >> > >> >> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> > >> >> >> --- > >> >> >> drivers/gpu/drm/drm_fourcc.c | 3 +++ > >> >> >> 1 file changed, 3 insertions(+) > >> >> >> > >> >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > >> >> >> index 90d2cc8..0a3ff0b 100644 > >> >> >> --- a/drivers/gpu/drm/drm_fourcc.c > >> >> >> +++ b/drivers/gpu/drm/drm_fourcc.c > >> >> >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); > >> >> >> */ > >> >> >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) > >> >> >> { > >> >> >> + if (!buf) > >> >> >> + return NULL; > >> >> >> + > >> >> > > >> >> > Seems rather pointless to me. Why would you ever pass NULL to this guy? I don't know, maybe because I'm a malicious driver writer that wants to crash the kernel? The function is exported, so it can be called by any module, even out-of-tree. Looks like an easy DoS to me. > >> >> > >> >> perhaps BUG_ON(!buf)... > >> > > >> > And how does that differ from just buf->foo? > >> > >> it gets you a file and line # in the error splat.. not that > >> drm_get_format_name() is such a big function that it would be > >> difficult to decipher the null deref crash, but if we added anything > >> it should be BUG_ON() to make it clear that passing null isn't a > >> caller error. > > > > Yeah, BUG_ON() at least documents the intent, so it's better than > > the null check. But for something like this even BUG_ON() is > > just wasted bytes IMO. > > +1 > > The patch has a Fixes line, but AFAICT, the referenced patch didn't > introduce any NULL opportunities that weren't previously there. Really? Before the referenced patch the function only had one parameter, an uint32_t. True that kmalloc could return a NULL pointer and we would've crashed there as well, but at least we were running out of memory. Now I can crash the kernel any time I want with a badly written driver/module. Best regards, Liviu > > Sean > > > > > > BUG_ON() can be useful for those weird bugs where somewhere deep > > down you hit a null pointer and you can't figure out where the > > bad pointer came from. So you might sprinkle a few BUG_ONs() > > further up to catch it sooner. Esp. if you can't reproduce the > > bug yourself and have to rely on user(s) to find it for you. > > > > Even WARN_ON() w/ or w/o an early bailout might be a decent idea > > sometimes since it might have a slightly higher chance of keeping > > the kernel in working condition, but IMO just blindly throwing > > it around everywhere is not a good approach. > > > > -- > > Ville Syrjälä > > Intel OTC > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: > On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä > <ville.syrjala@linux.intel.com> wrote: > > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: > >> drm_get_format_name() de-references the buf parameter without checking > >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets > >> sanitise the parameters before proceeding. > >> > >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) > >> Cc: Eric Engestrom <eric@engestrom.ch> > >> Cc: Rob Clark <robdclark@gmail.com> > >> Cc: Jani Nikula <jani.nikula@intel.com> > >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > >> > >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> > >> --- > >> drivers/gpu/drm/drm_fourcc.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > >> index 90d2cc8..0a3ff0b 100644 > >> --- a/drivers/gpu/drm/drm_fourcc.c > >> +++ b/drivers/gpu/drm/drm_fourcc.c > >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); > >> */ > >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) > >> { > >> + if (!buf) > >> + return NULL; > >> + > > > > Seems rather pointless to me. Why would you ever pass NULL to this guy? > > perhaps BUG_ON(!buf)... Nah, I don't want to start spamming the logs. You passed nothing, you get nothing, no reason to throw a tantrum. Best regards, Liviu > > BR, > -R > > >> snprintf(buf->str, sizeof(buf->str), > >> "%c%c%c%c %s-endian (0x%08x)", > >> printable_char(format & 0xff), > >> -- > >> 2.10.2 > >> > >> _______________________________________________ > >> dri-devel mailing list > >> dri-devel@lists.freedesktop.org > >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- > > Ville Syrjälä > > Intel OTC > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Tue, Nov 22, 2016 at 1:47 PM, Liviu Dudau <Liviu.Dudau@arm.com> wrote: > On Tue, Nov 22, 2016 at 01:15:08PM -0500, Sean Paul wrote: >> On Tue, Nov 22, 2016 at 1:06 PM, Ville Syrjälä >> <ville.syrjala@linux.intel.com> wrote: >> > On Tue, Nov 22, 2016 at 12:35:53PM -0500, Rob Clark wrote: >> >> On Tue, Nov 22, 2016 at 12:31 PM, Ville Syrjälä >> >> <ville.syrjala@linux.intel.com> wrote: >> >> > On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: >> >> >> On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrjälä >> >> >> <ville.syrjala@linux.intel.com> wrote: >> >> >> > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: >> >> >> >> drm_get_format_name() de-references the buf parameter without checking >> >> >> >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets >> >> >> >> sanitise the parameters before proceeding. >> >> >> >> >> >> >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) >> >> >> >> Cc: Eric Engestrom <eric@engestrom.ch> >> >> >> >> Cc: Rob Clark <robdclark@gmail.com> >> >> >> >> Cc: Jani Nikula <jani.nikula@intel.com> >> >> >> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> >> >> >> >> >> >> >> >> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> >> >> >> >> --- >> >> >> >> drivers/gpu/drm/drm_fourcc.c | 3 +++ >> >> >> >> 1 file changed, 3 insertions(+) >> >> >> >> >> >> >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c >> >> >> >> index 90d2cc8..0a3ff0b 100644 >> >> >> >> --- a/drivers/gpu/drm/drm_fourcc.c >> >> >> >> +++ b/drivers/gpu/drm/drm_fourcc.c >> >> >> >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); >> >> >> >> */ >> >> >> >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) >> >> >> >> { >> >> >> >> + if (!buf) >> >> >> >> + return NULL; >> >> >> >> + >> >> >> > >> >> >> > Seems rather pointless to me. Why would you ever pass NULL to this guy? > > I don't know, maybe because I'm a malicious driver writer that wants to crash the kernel? > The function is exported, so it can be called by any module, even out-of-tree. Looks > like an easy DoS to me. if you are a kernel module, in tree or not, all bets are off.. an out of tree module could just as easily call sprintf(NULL, "foo") directly.. BR, -R >> >> >> >> >> >> perhaps BUG_ON(!buf)... >> >> > >> >> > And how does that differ from just buf->foo? >> >> >> >> it gets you a file and line # in the error splat.. not that >> >> drm_get_format_name() is such a big function that it would be >> >> difficult to decipher the null deref crash, but if we added anything >> >> it should be BUG_ON() to make it clear that passing null isn't a >> >> caller error. >> > >> > Yeah, BUG_ON() at least documents the intent, so it's better than >> > the null check. But for something like this even BUG_ON() is >> > just wasted bytes IMO. >> >> +1 >> >> The patch has a Fixes line, but AFAICT, the referenced patch didn't >> introduce any NULL opportunities that weren't previously there. > > Really? Before the referenced patch the function only had one parameter, > an uint32_t. True that kmalloc could return a NULL pointer and we would've > crashed there as well, but at least we were running out of memory. Now > I can crash the kernel any time I want with a badly written driver/module. > > Best regards, > Liviu > >> >> Sean >> >> >> > >> > BUG_ON() can be useful for those weird bugs where somewhere deep >> > down you hit a null pointer and you can't figure out where the >> > bad pointer came from. So you might sprinkle a few BUG_ONs() >> > further up to catch it sooner. Esp. if you can't reproduce the >> > bug yourself and have to rely on user(s) to find it for you. >> > >> > Even WARN_ON() w/ or w/o an early bailout might be a decent idea >> > sometimes since it might have a slightly higher chance of keeping >> > the kernel in working condition, but IMO just blindly throwing >> > it around everywhere is not a good approach. >> > >> > -- >> > Ville Syrjälä >> > Intel OTC >> > _______________________________________________ >> > dri-devel mailing list >> > dri-devel@lists.freedesktop.org >> > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > -- > ==================== > | I would like to | > | fix the world, | > | but they're not | > | giving me the | > \ source code! / > --------------- > ¯\_(ツ)_/¯
diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c index 90d2cc8..0a3ff0b 100644 --- a/drivers/gpu/drm/drm_fourcc.c +++ b/drivers/gpu/drm/drm_fourcc.c @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); */ const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) { + if (!buf) + return NULL; + snprintf(buf->str, sizeof(buf->str), "%c%c%c%c %s-endian (0x%08x)", printable_char(format & 0xff),
drm_get_format_name() de-references the buf parameter without checking if the pointer was not NULL. Given that the function is EXPORT-ed, lets sanitise the parameters before proceeding. Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) Cc: Eric Engestrom <eric@engestrom.ch> Cc: Rob Clark <robdclark@gmail.com> Cc: Jani Nikula <jani.nikula@intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com> --- drivers/gpu/drm/drm_fourcc.c | 3 +++ 1 file changed, 3 insertions(+)