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Tue, 15 Nov 2022 22:16:42 +0000 (UTC) Date: Wed, 16 Nov 2022 07:16:27 +0900 From: asmadeus@codewreck.org To: Peng Zhang Cc: ericvh@gmail.com, lucho@ionkov.net, linux_oss@crudebyte.com, dhowells@redhat.com, jlayton@kernel.org, v9fs-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org, syzbot+a76f6a6e524cf2080aa3@syzkaller.appspotmail.com Subject: Re: [PATCH v2] fscache: fix OOB Read in __fscache_acquire_volume Message-ID: References: <20221115140447.2971680-1-zhangpeng362@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221115140447.2971680-1-zhangpeng362@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peng Zhang wrote on Tue, Nov 15, 2022 at 02:04:47PM +0000: > From: ZhangPeng > > Syzbot reported slab-out-of-bounds Read in __fscache_acquire_volume. > > ================================================================== > 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: > > __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 > ================================================================== > > 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. Fix this by adding a check on the length of the key > in fscache_alloc_volume(). > --- > v1 -> v2: > - Make sure the length of cache volume key (klen) fits a signed char > before writing key[0] that'd benefit everyone, thanks to Dominique > Martinet. > > Reported-by: syzbot+a76f6a6e524cf2080aa3@syzkaller.appspotmail.com > Fixes: 62ab63352350 ("fscache: Implement volume registration") > Signed-off-by: ZhangPeng These tags should go above the '---' line, or git am will be confused and drop them. (I assume David or whoever picks this up can manually fix this, letting them comment) That aside: Acked-by: Dominique Martinet > --- > fs/fscache/volume.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c > index a058e0136bfe..cc206d5e4cc7 100644 > --- a/fs/fscache/volume.c > +++ b/fs/fscache/volume.c > @@ -230,6 +230,8 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key, > * hashing easier. > */ > klen = strlen(volume_key); > + if (klen > 127) > + goto err_cache; > hlen = round_up(1 + klen + 1, sizeof(__le32)); > key = kzalloc(hlen, GFP_KERNEL); > if (!key) -- Dominique