WARNING: kmalloc bug in bfs_fill_super

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Mar 30, 2018, 4:01:03 PM3/30/18
to aivazia...@gmail.com, linux-...@vger.kernel.org, syzkall...@googlegroups.com

syzbot hit the following crash on upstream commit
9dd2326890d89a5179967c947dab2bab34d7ddee (Fri Mar 30 17:29:47 2018 +0000)
Merge tag 'ceph-for-4.16-rc8' of git://github.com/ceph/ceph-client
syzbot dashboard link:

So far this crash happened 2 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=4931648743276544
syzkaller reproducer:
Raw console output:
Kernel config:
compiler: gcc (GCC) 7.1.1 20170620

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Reported-by: syzbot+71c6b5...@syzkaller.appspotmail.com
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BFS-fs: bfs_fill_super(): loop0 is unclean, continuing
WARNING: CPU: 1 PID: 4468 at mm/slab_common.c:1012 kmalloc_slab+0x5d/0x70
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 4468 Comm: syzkaller458727 Not tainted 4.16.0-rc7+ #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
panic+0x1e4/0x41c kernel/panic.c:183
__warn+0x1dc/0x200 kernel/panic.c:547
report_bug+0x1f4/0x2b0 lib/bug.c:186
fixup_bug.part.10+0x37/0x80 arch/x86/kernel/traps.c:178
fixup_bug arch/x86/kernel/traps.c:247 [inline]
do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:986
RIP: 0010:kmalloc_slab+0x5d/0x70 mm/slab_common.c:1012
RSP: 0018:ffff8801ad117908 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801b904e004 RCX: ffffffff820931da
RDX: 1ffff1003a1dfac4 RSI: 0000000000000000 RDI: 0000000000800000
RBP: ffff8801ad117908 R08: 1ffff10035a22e81 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000007fffff
R13: ffff8801b904e000 R14: 00000000014080c0 R15: ffff8801d9194cc0
__do_kmalloc mm/slab.c:3701 [inline]
__kmalloc+0x25/0x760 mm/slab.c:3715
kmalloc include/linux/slab.h:517 [inline]
kzalloc include/linux/slab.h:701 [inline]
bfs_fill_super+0x3d3/0xea0 fs/bfs/inode.c:362
mount_bdev+0x2b7/0x370 fs/super.c:1119
bfs_mount+0x34/0x40 fs/bfs/inode.c:465
mount_fs+0x66/0x2d0 fs/super.c:1222
vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:2509 [inline]
do_new_mount fs/namespace.c:2512 [inline]
do_mount+0xea4/0x2bb0 fs/namespace.c:2842
SYSC_mount fs/namespace.c:3058 [inline]
SyS_mount+0xab/0x120 fs/namespace.c:3035
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
RIP: 0033:0x442d3a
RSP: 002b:00007ffd0d12ac38 EFLAGS: 00000297 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000442d3a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007ffd0d12ac40
RBP: 0000000000000004 R08: 0000000000000000 R09: 000000000000000a
R10: 00000000c0ed0000 R11: 0000000000000297 R12: 0000000000401ba0
R13: 0000000000401c30 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..

This bug is generated by a dumb bot. It may contain errors.
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Tetsuo Handa

May 1, 2018, 6:01:22 AM5/1/18
to syzbot, aivazia...@gmail.com, linux-...@vger.kernel.org, syzkall...@googlegroups.com
From 247cae4da0490c2e285e0a99e630ef963fabb6d5 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
Date: Tue, 1 May 2018 14:15:19 +0900
Subject: [PATCH] bfs: add sanity check at bfs_fill_super().

syzbot is reporting too large memory allocation at bfs_fill_super() [1].
Since file system image is corrupted such that bfs_sb->s_start == 0,
bfs_fill_super() is trying to allocate 8MB of continuous memory. Fix this
by adding a sanity check on bfs_sb->s_start, __GFP_NOWARN and printf().

[1] https://syzkaller.appspot.com/bug?id=16a87c236b951351374a84c8a32f40edbc034e96

Signed-off-by: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+71c6b5...@syzkaller.appspotmail.com>
Cc: Tigran A. Aivazian <aivazia...@gmail.com>
fs/bfs/inode.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
index 9a69392..d81c148 100644
--- a/fs/bfs/inode.c
+++ b/fs/bfs/inode.c
@@ -350,7 +350,8 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)

s->s_magic = BFS_MAGIC;

- if (le32_to_cpu(bfs_sb->s_start) > le32_to_cpu(bfs_sb->s_end)) {
+ if (le32_to_cpu(bfs_sb->s_start) > le32_to_cpu(bfs_sb->s_end) ||
+ le32_to_cpu(bfs_sb->s_start) < BFS_BSIZE) {
printf("Superblock is corrupted\n");
goto out1;
@@ -359,9 +360,11 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
sizeof(struct bfs_inode)
imap_len = (info->si_lasti / 8) + 1;
- info->si_imap = kzalloc(imap_len, GFP_KERNEL);
- if (!info->si_imap)
+ info->si_imap = kzalloc(imap_len, GFP_KERNEL | __GFP_NOWARN);
+ if (!info->si_imap) {
+ printf("Cannot allocate %u bytes\n", imap_len);
goto out1;
+ }
for (i = 0; i < BFS_ROOT_INO; i++)
set_bit(i, info->si_imap);


Tigran Aivazian

May 1, 2018, 6:45:34 AM5/1/18
to Tetsuo Handa, syzbot, LKML, syzkall...@googlegroups.com
Looks good to me, thank you.
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