| Message ID | 20200427020212.5222-1-longman@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/slub: Fix incorrect checkings of s->offset | expand |
On Sun, Apr 26, 2020 at 10:02:12PM -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 to appear with > the system in panic afterwards. > > To fix it, use the check "s->offset == s->inuse" instead. I think a little refactoring would make this more clear. unsigned int track_offset(const struct kmem_cache *s) { return s->inuse + (s->offset == s->inuse) ? sizeof(void *) : 0; } > @@ -556,10 +556,8 @@ static struct track *get_track(struct kmem_cache *s, void *object, > { > struct track *p; > > - if (s->offset) > - p = object + s->offset + sizeof(void *); > - else > - p = object + s->inuse; > + p = object + s->inuse + > + ((s->offset == s->inuse) ? sizeof(void *) : 0); p = object + track_offset(s); > return p + alloc; > } > @@ -693,10 +691,8 @@ 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 = s->inuse + > + ((s->offset == s->inuse) ? sizeof(void *) : 0); off = track_offset(s); > @@ -826,7 +822,7 @@ 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) > + if (s->offset == s->inuse) > /* Freepointer is placed after the object. */ > off += sizeof(void *); unsigned long off = track_offset(s);
On 4/27/20 8:38 AM, Matthew Wilcox wrote: > On Sun, Apr 26, 2020 at 10:02:12PM -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 to appear with >> the system in panic afterwards. >> >> To fix it, use the check "s->offset == s->inuse" instead. > I think a little refactoring would make this more clear. > > unsigned int track_offset(const struct kmem_cache *s) > { > return s->inuse + (s->offset == s->inuse) ? sizeof(void *) : 0; > } Yes, that was what I am thinking of doing in v2. Thanks, Longman
On 4/27/20 9:18 AM, Waiman Long wrote: > On 4/27/20 8:38 AM, Matthew Wilcox wrote: >> On Sun, Apr 26, 2020 at 10:02:12PM -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 to appear with >>> the system in panic afterwards. >>> >>> To fix it, use the check "s->offset == s->inuse" instead. >> I think a little refactoring would make this more clear. >> >> unsigned int track_offset(const struct kmem_cache *s) >> { >> return s->inuse + (s->offset == s->inuse) ? sizeof(void *) : 0; >> } > > Yes, that was what I am thinking of doing in v2. BTW, "+" has a higher priority than "?:". So we need a parenthesis around "?:". Cheers, Longman
On Mon, Apr 27, 2020 at 09:29:41AM -0400, Waiman Long wrote: > On 4/27/20 9:18 AM, Waiman Long wrote: > > On 4/27/20 8:38 AM, Matthew Wilcox wrote: > > > On Sun, Apr 26, 2020 at 10:02:12PM -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 to appear with > > > > the system in panic afterwards. > > > > > > > > To fix it, use the check "s->offset == s->inuse" instead. > > > I think a little refactoring would make this more clear. > > > > > > unsigned int track_offset(const struct kmem_cache *s) > > > { > > > return s->inuse + (s->offset == s->inuse) ? sizeof(void *) : 0; > > > } > > > > Yes, that was what I am thinking of doing in v2. > > BTW, "+" has a higher priority than "?:". So we need a parenthesis around > "?:". That seems like a good reason to not use ?: unsigned int track_offset(const struct kmem_cache *s) { if (s->offset != s->inuse) return s->inuse; return s->inuse + sizeof(void *); } Also this needs a comment about why we're doing this ... something about the freelist pointer, I think?
On 4/27/20 9:38 AM, Matthew Wilcox wrote: > On Mon, Apr 27, 2020 at 09:29:41AM -0400, Waiman Long wrote: >> On 4/27/20 9:18 AM, Waiman Long wrote: >>> On 4/27/20 8:38 AM, Matthew Wilcox wrote: >>>> On Sun, Apr 26, 2020 at 10:02:12PM -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 to appear with >>>>> the system in panic afterwards. >>>>> >>>>> To fix it, use the check "s->offset == s->inuse" instead. >>>> I think a little refactoring would make this more clear. >>>> >>>> unsigned int track_offset(const struct kmem_cache *s) >>>> { >>>> return s->inuse + (s->offset == s->inuse) ? sizeof(void *) : 0; >>>> } >>> Yes, that was what I am thinking of doing in v2. >> BTW, "+" has a higher priority than "?:". So we need a parenthesis around >> "?:". > That seems like a good reason to not use ?: > > unsigned int track_offset(const struct kmem_cache *s) > { > if (s->offset != s->inuse) > return s->inuse; > return s->inuse + sizeof(void *); > } > > Also this needs a comment about why we're doing this ... something about > the freelist pointer, I think? > I can see a simple if-else to make it easier to read. Thanks, Longman
diff --git a/mm/slub.c b/mm/slub.c index 0e736d66bb42..99952d01e7e0 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -556,10 +556,8 @@ static struct track *get_track(struct kmem_cache *s, void *object, { struct track *p; - if (s->offset) - p = object + s->offset + sizeof(void *); - else - p = object + s->inuse; + p = object + s->inuse + + ((s->offset == s->inuse) ? sizeof(void *) : 0); return p + alloc; } @@ -693,10 +691,8 @@ 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 = s->inuse + + ((s->offset == s->inuse) ? sizeof(void *) : 0); if (s->flags & SLAB_STORE_USER) off += 2 * sizeof(struct track); @@ -790,7 +786,7 @@ 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) @@ -826,7 +822,7 @@ 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) + if (s->offset == s->inuse) /* Freepointer is placed after the object. */ off += sizeof(void *); @@ -915,7 +911,7 @@ 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 ((s->offset != s->inuse) && val == SLUB_RED_ACTIVE) /* * Object and freepointer overlap. Cannot check * freepointer while object is allocated.
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 to appear with the system in panic afterwards. To fix it, use the check "s->offset == s->inuse" instead. Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") Signed-off-by: Waiman Long <longman@redhat.com> --- mm/slub.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-)