| Message ID | 20200429135328.26976-1-longman@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] mm/slub: Fix incorrect interpretation of s->offset | expand |
On 4/29/20 9:53 AM, Waiman Long wrote: > In a couple of places in the slub memory allocator, the code uses > "s->offset" as a check to see if the free pointer is put right after the > object. That check is no longer true with commit 3202fa62fb43 ("slub: > relocate freelist pointer to middle of object"). > > As a result, echoing "1" into the validate sysfs file, e.g. of dentry, > may cause a bunch of "Freepointer corrupt" error reports like the > following to appear with the system in panic afterwards. > > [ 38.579769] ============================================================================= > [ 38.580845] BUG dentry(666:pmcd.service) (Tainted: G B): Freepointer corrupt > [ 38.581948] ----------------------------------------------------------------------------- > > To fix it, use the check "s->offset == s->inuse" in the new helper Sorry, forgot to change the commit log to ">=". Anyway, this is a serious bug that needs to be fixed before v5.7 is released. Cheers, Longman
On Wed, Apr 29, 2020 at 09:53:28AM -0400, Waiman Long wrote: > As a result, echoing "1" into the validate sysfs file, e.g. of dentry, > may cause a bunch of "Freepointer corrupt" error reports like the > following to appear with the system in panic afterwards. > > [ 38.579769] ============================================================================= > [ 38.580845] BUG dentry(666:pmcd.service) (Tainted: G B): Freepointer corrupt > [ 38.581948] ----------------------------------------------------------------------------- I might trim the timestamp and the === and --- from the commit message ... > To fix it, use the check "s->offset == s->inuse" in the new helper > function freeptr_outside_object() instead. Also add another helper function > get_info_end() to return the end of info block (inuse + free pointer > if not overlapping with object). > > Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") > Signed-off-by: Waiman Long <longman@redhat.com> But the patch looks great. Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> In a couple of places in the slub memory allocator, the code uses > "s->offset" as a check to see if the free pointer is put right after the > object. That check is no longer true with commit 3202fa62fb43 ("slub: > relocate freelist pointer to middle of object"). Will any further collateral evolution become interesting? … > +++ b/mm/slub.c > @@ -551,15 +551,32 @@ static void print_section(char *level, char *text, u8 *addr, … > +static inline unsigned int get_info_end(struct kmem_cache *s) > +{ > + if (freeptr_outside_object(s)) > + return s->inuse + sizeof(void *); > + else > + return s->inuse; > +} How do you think about the following source code variants? + return freeptr_outside_object(s) + ? s->inuse + sizeof(void *) + : s->inuse; > static struct track *get_track(struct kmem_cache *s, void *object, > enum track_item alloc) > { > struct track *p; > > - if (s->offset) > - p = object + s->offset + sizeof(void *); > - else > - p = object + s->inuse; > + p = object + get_info_end(s); > > return p + alloc; > } + struct track *p = object + get_info_end(s); return p + alloc; Regards, Markus
On Wed, Apr 29, 2020 at 06:42:55PM +0200, Markus Elfring wrote: > > In a couple of places in the slub memory allocator, the code uses > > "s->offset" as a check to see if the free pointer is put right after the > > object. That check is no longer true with commit 3202fa62fb43 ("slub: > > relocate freelist pointer to middle of object"). > > Will any further collateral evolution become interesting? What do you mean by this question? > > +static inline unsigned int get_info_end(struct kmem_cache *s) > > +{ > > + if (freeptr_outside_object(s)) > > + return s->inuse + sizeof(void *); > > + else > > + return s->inuse; > > +} > > How do you think about the following source code variants? > > + return freeptr_outside_object(s) > + ? s->inuse + sizeof(void *) > + : s->inuse; That is less clear than the version Wayman posted. > > static struct track *get_track(struct kmem_cache *s, void *object, > > enum track_item alloc) > > { > > struct track *p; > > > > - if (s->offset) > > - p = object + s->offset + sizeof(void *); > > - else > > - p = object + s->inuse; > > + p = object + get_info_end(s); > > > > return p + alloc; > > } > > + struct track *p = object + get_info_end(s); > > return p + alloc; Yes, I think that's an improvement.
On Wed, Apr 29, 2020 at 09:53:28AM -0400, Waiman Long wrote: > In a couple of places in the slub memory allocator, the code uses > "s->offset" as a check to see if the free pointer is put right after the > object. That check is no longer true with commit 3202fa62fb43 ("slub: > relocate freelist pointer to middle of object"). > > As a result, echoing "1" into the validate sysfs file, e.g. of dentry, > may cause a bunch of "Freepointer corrupt" error reports like the > following to appear with the system in panic afterwards. > > [ 38.579769] ============================================================================= > [ 38.580845] BUG dentry(666:pmcd.service) (Tainted: G B): Freepointer corrupt > [ 38.581948] ----------------------------------------------------------------------------- > > To fix it, use the check "s->offset == s->inuse" in the new helper > function freeptr_outside_object() instead. Also add another helper function > get_info_end() to return the end of info block (inuse + free pointer > if not overlapping with object). > > Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") > Signed-off-by: Waiman Long <longman@redhat.com> > --- > mm/slub.c | 45 ++++++++++++++++++++++++++++++--------------- > 1 file changed, 30 insertions(+), 15 deletions(-) > > [v3: Change function name to freeptr_outside_object(), update check & add comment] > > diff --git a/mm/slub.c b/mm/slub.c > index 9bf44955c4f1..b762450fc9f0 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -551,15 +551,32 @@ static void print_section(char *level, char *text, u8 *addr, > metadata_access_disable(); > } > > +/* > + * See comment in calculate_sizes(). > + */ > +static inline bool freeptr_outside_object(struct kmem_cache *s) > +{ > + return s->offset >= s->inuse; > +} > + > +/* > + * Return offset of the end of info block which is inuse + free pointer if > + * not overlapping with object. > + */ > +static inline unsigned int get_info_end(struct kmem_cache *s) > +{ > + if (freeptr_outside_object(s)) > + return s->inuse + sizeof(void *); > + else > + return s->inuse; > +} > + > static struct track *get_track(struct kmem_cache *s, void *object, > enum track_item alloc) > { > struct track *p; > > - if (s->offset) > - p = object + s->offset + sizeof(void *); > - else > - p = object + s->inuse; > + p = object + get_info_end(s); > > return p + alloc; > } > @@ -686,10 +703,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p) > print_section(KERN_ERR, "Redzone ", p + s->object_size, > s->inuse - s->object_size); > > - if (s->offset) > - off = s->offset + sizeof(void *); > - else > - off = s->inuse; > + off = get_info_end(s); > > if (s->flags & SLAB_STORE_USER) > off += 2 * sizeof(struct track); > @@ -782,7 +796,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, > * object address > * Bytes of the object to be managed. > * If the freepointer may overlay the object then the free > - * pointer is the first word of the object. > + * pointer is at the middle of the object. > * > * Poisoning uses 0x6b (POISON_FREE) and the last byte is > * 0xa5 (POISON_END) > @@ -816,11 +830,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, > > static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p) > { > - unsigned long off = s->inuse; /* The end of info */ > - > - if (s->offset) > - /* Freepointer is placed after the object. */ > - off += sizeof(void *); > + unsigned long off = get_info_end(s); /* The end of info */ > > if (s->flags & SLAB_STORE_USER) > /* We also have user information there */ > @@ -907,7 +917,7 @@ static int check_object(struct kmem_cache *s, struct page *page, > check_pad_bytes(s, page, p); > } > > - if (!s->offset && val == SLUB_RED_ACTIVE) > + if (!freeptr_outside_object(s) && val == SLUB_RED_ACTIVE) > /* > * Object and freepointer overlap. Cannot check > * freepointer while object is allocated. > @@ -3587,6 +3597,11 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) > * > * This is the case if we do RCU, have a constructor or > * destructor or are poisoning the objects. > + * > + * The assumption that s->offset >= s->inuse means free > + * pointer is outside of the object is used in the > + * freeptr_outside_object() function. If that is no > + * longer true, the function needs to be modified. > */ > s->offset = size; > size += sizeof(void *); > -- > 2.18.1 > > Acked-by: Rafael Aquini <aquini@redhat.com>
On Wed, Apr 29, 2020 at 09:53:28AM -0400, Waiman Long wrote: > In a couple of places in the slub memory allocator, the code uses > "s->offset" as a check to see if the free pointer is put right after the > object. That check is no longer true with commit 3202fa62fb43 ("slub: > relocate freelist pointer to middle of object"). > > As a result, echoing "1" into the validate sysfs file, e.g. of dentry, > may cause a bunch of "Freepointer corrupt" error reports like the > following to appear with the system in panic afterwards. > > [ 38.579769] ============================================================================= > [ 38.580845] BUG dentry(666:pmcd.service) (Tainted: G B): Freepointer corrupt > [ 38.581948] ----------------------------------------------------------------------------- > > To fix it, use the check "s->offset == s->inuse" in the new helper > function freeptr_outside_object() instead. Also add another helper function > get_info_end() to return the end of info block (inuse + free pointer > if not overlapping with object). > > Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") > Signed-off-by: Waiman Long <longman@redhat.com> Thanks! Nice catch. :) Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > --- > mm/slub.c | 45 ++++++++++++++++++++++++++++++--------------- > 1 file changed, 30 insertions(+), 15 deletions(-) > > [v3: Change function name to freeptr_outside_object(), update check & add comment] > > diff --git a/mm/slub.c b/mm/slub.c > index 9bf44955c4f1..b762450fc9f0 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -551,15 +551,32 @@ static void print_section(char *level, char *text, u8 *addr, > metadata_access_disable(); > } > > +/* > + * See comment in calculate_sizes(). > + */ > +static inline bool freeptr_outside_object(struct kmem_cache *s) > +{ > + return s->offset >= s->inuse; > +} > + > +/* > + * Return offset of the end of info block which is inuse + free pointer if > + * not overlapping with object. > + */ > +static inline unsigned int get_info_end(struct kmem_cache *s) > +{ > + if (freeptr_outside_object(s)) > + return s->inuse + sizeof(void *); > + else > + return s->inuse; > +} > + > static struct track *get_track(struct kmem_cache *s, void *object, > enum track_item alloc) > { > struct track *p; > > - if (s->offset) > - p = object + s->offset + sizeof(void *); > - else > - p = object + s->inuse; > + p = object + get_info_end(s); > > return p + alloc; > } > @@ -686,10 +703,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p) > print_section(KERN_ERR, "Redzone ", p + s->object_size, > s->inuse - s->object_size); > > - if (s->offset) > - off = s->offset + sizeof(void *); > - else > - off = s->inuse; > + off = get_info_end(s); > > if (s->flags & SLAB_STORE_USER) > off += 2 * sizeof(struct track); > @@ -782,7 +796,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, > * object address > * Bytes of the object to be managed. > * If the freepointer may overlay the object then the free > - * pointer is the first word of the object. > + * pointer is at the middle of the object. > * > * Poisoning uses 0x6b (POISON_FREE) and the last byte is > * 0xa5 (POISON_END) > @@ -816,11 +830,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, > > static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p) > { > - unsigned long off = s->inuse; /* The end of info */ > - > - if (s->offset) > - /* Freepointer is placed after the object. */ > - off += sizeof(void *); > + unsigned long off = get_info_end(s); /* The end of info */ > > if (s->flags & SLAB_STORE_USER) > /* We also have user information there */ > @@ -907,7 +917,7 @@ static int check_object(struct kmem_cache *s, struct page *page, > check_pad_bytes(s, page, p); > } > > - if (!s->offset && val == SLUB_RED_ACTIVE) > + if (!freeptr_outside_object(s) && val == SLUB_RED_ACTIVE) > /* > * Object and freepointer overlap. Cannot check > * freepointer while object is allocated. > @@ -3587,6 +3597,11 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) > * > * This is the case if we do RCU, have a constructor or > * destructor or are poisoning the objects. > + * > + * The assumption that s->offset >= s->inuse means free > + * pointer is outside of the object is used in the > + * freeptr_outside_object() function. If that is no > + * longer true, the function needs to be modified. > */ > s->offset = size; > size += sizeof(void *); > -- > 2.18.1 >
diff --git a/mm/slub.c b/mm/slub.c index 9bf44955c4f1..b762450fc9f0 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -551,15 +551,32 @@ static void print_section(char *level, char *text, u8 *addr, metadata_access_disable(); } +/* + * See comment in calculate_sizes(). + */ +static inline bool freeptr_outside_object(struct kmem_cache *s) +{ + return s->offset >= s->inuse; +} + +/* + * Return offset of the end of info block which is inuse + free pointer if + * not overlapping with object. + */ +static inline unsigned int get_info_end(struct kmem_cache *s) +{ + if (freeptr_outside_object(s)) + return s->inuse + sizeof(void *); + else + return s->inuse; +} + static struct track *get_track(struct kmem_cache *s, void *object, enum track_item alloc) { struct track *p; - if (s->offset) - p = object + s->offset + sizeof(void *); - else - p = object + s->inuse; + p = object + get_info_end(s); return p + alloc; } @@ -686,10 +703,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p) print_section(KERN_ERR, "Redzone ", p + s->object_size, s->inuse - s->object_size); - if (s->offset) - off = s->offset + sizeof(void *); - else - off = s->inuse; + off = get_info_end(s); if (s->flags & SLAB_STORE_USER) off += 2 * sizeof(struct track); @@ -782,7 +796,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, * object address * Bytes of the object to be managed. * If the freepointer may overlay the object then the free - * pointer is the first word of the object. + * pointer is at the middle of the object. * * Poisoning uses 0x6b (POISON_FREE) and the last byte is * 0xa5 (POISON_END) @@ -816,11 +830,7 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page, static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p) { - unsigned long off = s->inuse; /* The end of info */ - - if (s->offset) - /* Freepointer is placed after the object. */ - off += sizeof(void *); + unsigned long off = get_info_end(s); /* The end of info */ if (s->flags & SLAB_STORE_USER) /* We also have user information there */ @@ -907,7 +917,7 @@ static int check_object(struct kmem_cache *s, struct page *page, check_pad_bytes(s, page, p); } - if (!s->offset && val == SLUB_RED_ACTIVE) + if (!freeptr_outside_object(s) && val == SLUB_RED_ACTIVE) /* * Object and freepointer overlap. Cannot check * freepointer while object is allocated. @@ -3587,6 +3597,11 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) * * This is the case if we do RCU, have a constructor or * destructor or are poisoning the objects. + * + * The assumption that s->offset >= s->inuse means free + * pointer is outside of the object is used in the + * freeptr_outside_object() function. If that is no + * longer true, the function needs to be modified. */ s->offset = size; size += sizeof(void *);
In a couple of places in the slub memory allocator, the code uses "s->offset" as a check to see if the free pointer is put right after the object. That check is no longer true with commit 3202fa62fb43 ("slub: relocate freelist pointer to middle of object"). As a result, echoing "1" into the validate sysfs file, e.g. of dentry, may cause a bunch of "Freepointer corrupt" error reports like the following to appear with the system in panic afterwards. [ 38.579769] ============================================================================= [ 38.580845] BUG dentry(666:pmcd.service) (Tainted: G B): Freepointer corrupt [ 38.581948] ----------------------------------------------------------------------------- To fix it, use the check "s->offset == s->inuse" in the new helper function freeptr_outside_object() instead. Also add another helper function get_info_end() to return the end of info block (inuse + free pointer if not overlapping with object). Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") Signed-off-by: Waiman Long <longman@redhat.com> --- mm/slub.c | 45 ++++++++++++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 15 deletions(-) [v3: Change function name to freeptr_outside_object(), update check & add comment]