fscache_set_key() seems to have 2 issues related to the memory read for hashing in fscache_set_key. The first reported was a KASAN error, BUG: KASAN: slab-out-of-bounds in fscache_alloc_cookie+0x5b3/0x680 [fscache] Read of size 4 at addr ffff88084ff056d4 by task mount.nfs/32615 also reported by syzbot at https://lkml.org/lkml/2018/7/8/236 BUG: KASAN: slab-out-of-bounds in fscache_set_key fs/fscache/cookie.c:120 [inline] BUG: KASAN: slab-out-of-bounds in fscache_alloc_cookie+0x7a9/0x880 fs/fscache/cookie.c:171 Read of size 4 at addr ffff8801d3cc8bb4 by task syz-executor907/4466 This happens for any index_key_len which is not divisible by 4, and is larger than the size of the inline key, because the code allocates exactly index_key_len for the key buffer, but the hashing loop is stepping through it 4 bytes (u32) at a time in the buf[] array. When looking over this, it also appears that the inline key is insufficiently initialized, zeroing only 3 of the 4 slots. Hence an index_key_len between 13 and 15 bytes will end up hashing uninitialized memory because the memcpy only partially fills the last buf[] element. Fix this by calculating how many u32 buffers we'll need by using DIV_ROUND_UP, and memset them all to zero before copying in the index_key, then using that same count as the hashing index limit. Reported-by: syzbot+a95b989b2dde8e806af8@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> --- nb: compile-tested only, sorry. diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c index 83bfe04..bc74ae3 100644 --- a/fs/fscache/cookie.c +++ b/fs/fscache/cookie.c @@ -83,7 +83,7 @@ void fscache_cookie_init_once(void *_cookie) } /* - * Set the index key in a cookie. The cookie struct has space for a 12-byte + * Set the index key in a cookie. The cookie struct has space for a 16-byte * key plus length and hash, but if that's not big enough, it's instead a * pointer to a buffer containing 3 bytes of hash, 1 byte of length and then * the key data. @@ -93,22 +93,22 @@ static int fscache_set_key(struct fscache_cookie *cookie, { unsigned long long h; u32 *buf; + int bufs; int i; cookie->key_len = index_key_len; + bufs = DIV_ROUND_UP(index_key_len, sizeof(*buf)); if (index_key_len > sizeof(cookie->inline_key)) { - buf = kzalloc(index_key_len, GFP_KERNEL); + buf = kmalloc_array(bufs, sizeof(*buf), GFP_KERNEL); if (!buf) return -ENOMEM; cookie->key = buf; } else { buf = (u32 *)cookie->inline_key; - buf[0] = 0; - buf[1] = 0; - buf[2] = 0; } + memset(buf, 0, bufs * sizeof(*buf)); memcpy(buf, index_key, index_key_len); /* Calculate a hash and combine this with the length in the first word @@ -116,7 +116,8 @@ static int fscache_set_key(struct fscache_cookie *cookie, */ h = (unsigned long)cookie->parent; h += index_key_len + cookie->type; - for (i = 0; i < (index_key_len + sizeof(u32) - 1) / sizeof(u32); i++) + + for (i = 0; i < bufs; i++) h += buf[i]; cookie->key_hash = h ^ (h >> 32);
