Thanks for your advice. The size needs to be able to hold up to 255 to handle larger keys. After testing, this patch works fine.From: ZhangPeng<zhangpeng362@xxxxxxxxxx> The type of a->key[0] is char in fscache_volume_same(). If the length of cache volume key is greater than 127, the value of a->key[0] is less than 0. In this case, klen becomes much larger than 255 after type conversion, because the type of klen is size_t. As a result, memcmp() is read out of bounds. This causes a slab-out-of-bounds Read in __fscache_acquire_volume(), as reported by Syzbot. Fix this by changing the type of the stored key to "u8 *" rather than "char *" (it isn't a simple string anyway). Also put in a check that the volume name doesn't exceed NAME_MAX. ================================================================== BUG: KASAN: slab-out-of-bounds in memcmp+0x16f/0x1c0 lib/string.c:757 Read of size 8 at addr ffff888016f3aa90 by task syz-executor344/3613 CPU: 0 PID: 3613 Comm: syz-executor344 Not tainted 6.0.0-rc2-syzkaller-00327-g8379c0b31fbc #0 Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022 Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_address_description mm/kasan/report.c:317 [inline] print_report.cold+0x2ba/0x719 mm/kasan/report.c:433 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495 memcmp+0x16f/0x1c0 lib/string.c:757 memcmp include/linux/fortify-string.h:420 [inline] fscache_volume_same fs/fscache/volume.c:133 [inline] fscache_hash_volume fs/fscache/volume.c:171 [inline] __fscache_acquire_volume+0x76c/0x1080 fs/fscache/volume.c:328 fscache_acquire_volume include/linux/fscache.h:204 [inline] v9fs_cache_session_get_cookie+0x143/0x240 fs/9p/cache.c:34 v9fs_session_init+0x1166/0x1810 fs/9p/v9fs.c:473 v9fs_mount+0xba/0xc90 fs/9p/vfs_super.c:126 legacy_get_tree+0x105/0x220 fs/fs_context.c:610 vfs_get_tree+0x89/0x2f0 fs/super.c:1530 do_new_mount fs/namespace.c:3040 [inline] path_mount+0x1326/0x1e20 fs/namespace.c:3370 do_mount fs/namespace.c:3383 [inline] __do_sys_mount fs/namespace.c:3591 [inline] __se_sys_mount fs/namespace.c:3568 [inline] __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f7d5064b1d9 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 14 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffd1700c028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 00007ffd1700c060 RCX: 00007f7d5064b1d9 RDX: 0000000020000040 RSI: 0000000020000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000020000200 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000f4240 R13: 0000000000000000 R14: 00007ffd1700c04c R15: 00007ffd1700c050 ================================================================== Fixes: 62ab63352350 ("fscache: Implement volume registration") Reported-by:syzbot+a76f6a6e524cf2080aa3@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: David Howells<dhowells@xxxxxxxxxx> cc: Peng Zhang<zhangpeng362@xxxxxxxxxx> cc: Dominique Martinet<asmadeus@xxxxxxxxxxxxx> cc: Jeff Layton<jlayton@xxxxxxxxxx> cc:v9fs-developer@xxxxxxxxxxxxxxxxxxxxx cc:linux-cachefs@xxxxxxxxxx Link:https://lore.kernel.org/r/Y3OH+Dmi0QIOK18n@xxxxxxxxxxxxx/ # Zhang Peng's v1 fix Link:https://lore.kernel.org/r/20221115140447.2971680-1-zhangpeng362@xxxxxxxxxx/ # Zhang Peng's v2 fix --- fs/fscache/volume.c | 7 +++++-- include/linux/fscache.h | 2 +- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c index a058e0136bfe..ab8ceddf9efa 100644 --- a/fs/fscache/volume.c +++ b/fs/fscache/volume.c @@ -203,7 +203,11 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key, struct fscache_volume *volume; struct fscache_cache *cache; size_t klen, hlen; - char *key; + u8 *key; + + klen = strlen(volume_key); + if (klen > NAME_MAX) + return NULL;if (!coherency_data)coherency_len = 0; @@ -229,7 +233,6 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key, /* Stick the length on the front of the key and pad it out to make * hashing easier. */ - klen = strlen(volume_key); hlen = round_up(1 + klen + 1, sizeof(__le32)); key = kzalloc(hlen, GFP_KERNEL); if (!key) diff --git a/include/linux/fscache.h b/include/linux/fscache.h index 36e5dd84cf59..8e312c8323a8 100644 --- a/include/linux/fscache.h +++ b/include/linux/fscache.h @@ -75,7 +75,7 @@ struct fscache_volume { atomic_t n_accesses; /* Number of cache accesses in progress */ unsigned int debug_id; unsigned int key_hash; /* Hash of key string */ - char *key; /* Volume ID, eg."afs@xxxxxxxxxxx@1234" */ + u8 *key; /* Volume ID, eg."afs@xxxxxxxxxxx@1234" */ struct list_head proc_link; /* Link in /proc/fs/fscache/volumes */ struct hlist_bl_node hash_link; /* Link in hash table */ struct work_struct work;
-- Zhang Peng -- Linux-cachefs mailing list Linux-cachefs@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/linux-cachefs
