linux-kernel - [PATCH] ext4: try to flush inline data before calling BUG in writepages

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Message-Id: <20220726224428.407887-1-tadeusz.struk@linaro.org>
Date:   Tue, 26 Jul 2022 15:44:28 -0700
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tadeusz Struk <tadeusz.struk@...aro.org>,
        syzbot+bd13648a53ed6933ca49@...kaller.appspotmail.com
Subject: [PATCH] ext4: try to flush inline data before calling BUG in writepages

Fix a syzbot issue, which triggers a BUG in ext4_writepags.
The syzbot creates and monuts an ext4 fs image on /dev/loop0.
The image is corrupted, which is probably the source of the
problems, but the mount operation finishes successfully.
Then the repro program creates a file on the mounted fs, and
eventually it writes a buff of 22 zero bytes to it as below:

memfd_create("syzkaller", 0) = 3
ftruncate(3, 2097152)       = 0
pwrite64(3, " \0\0\0\0\2\0\0\31\0\0\0\220\1\0\0\17\0\0\0\0\0\0\0\2\0\0\0\6\0\0\0"..., 102, 1024) = 102
pwrite64(3, "\0\0\0\0\0\0\0\0\0\0\0\0\202\343g$\306\363L\252\204n\322\345'p3x\1\0@", 31, 1248) = 31
pwrite64(3, "\2\0\0\0\3\0\0\0\4\0\0\0\31\0\17\0\3\0\4\0\0\0\0\0\0\0\0\0\17\0.i", 32, 4096) = 32
pwrite64(3, "\177\0\0\0\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377"..., 4098, 8192) = 4098
pwrite64(3, "\355A\0\0\20\0\0\0\332\364e_\333\364e_\333\364e_\0\0\0\0\0\0\4\0\200\0\0\0"..., 61, 17408) = 61
openat(AT_FDCWD, "/dev/loop0", O_RDWR) = 4
ioctl(4, LOOP_SET_FD, 3)    = 0
mkdir("./file0", 0777)      = -1 EEXIST (File exists)
mount("/dev/loop0", "./file0", "ext4", 0, ",errors=continue") = 0
openat(AT_FDCWD, "./file0", O_RDONLY|O_DIRECTORY) = 5
ioctl(4, LOOP_CLR_FD)       = 0
close(4)                    = 0
close(3)                    = 0
chdir("./file0")            = 0
creat("./bus", 000)         = 3
open("./bus", O_RDWR|O_CREAT|O_NONBLOCK|O_SYNC|O_DIRECT|O_LARGEFILE|O_NOATIME, 000) = 4
openat(AT_FDCWD, "/proc/self/exe", O_RDONLY) = 6
sendfile(4, 6, NULL, 2147483663) = 1638400
open("./bus", O_RDWR|O_CREAT|O_SYNC|O_NOATIME, 000) = 7
write(7, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 22) <unfinished ...>

This triggers a BUG in ext4_writepages(), where it checks if
the inode has inline data, just before deleting it:

kernel BUG at fs/ext4/inode.c:2721!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 359 Comm: repro Not tainted 5.19.0-rc8-00001-g31ba1e3b8305-dirty #15
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014
RIP: 0010:ext4_writepages+0x363d/0x3660
RSP: 0018:ffffc90000ccf260 EFLAGS: 00010293
RAX: ffffffff81e1abcd RBX: 0000008000000000 RCX: ffff88810842a180
RDX: 0000000000000000 RSI: 0000008000000000 RDI: 0000000000000000
RBP: ffffc90000ccf650 R08: ffffffff81e17d58 R09: ffffed10222c680b
R10: dfffe910222c680c R11: 1ffff110222c680a R12: ffff888111634128
R13: ffffc90000ccf880 R14: 0000008410000000 R15: 0000000000000001
FS:  00007f72635d2640(0000) GS:ffff88811b000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000565243379180 CR3: 000000010aa74000 CR4: 0000000000150eb0
Call Trace:
 <TASK>
 do_writepages+0x397/0x640
 filemap_fdatawrite_wbc+0x151/0x1b0
 file_write_and_wait_range+0x1c9/0x2b0
 ext4_sync_file+0x19e/0xa00
 vfs_fsync_range+0x17b/0x190
 ext4_buffered_write_iter+0x488/0x530
 ext4_file_write_iter+0x449/0x1b90
 vfs_write+0xbcd/0xf40
 ksys_write+0x198/0x2c0
 __x64_sys_write+0x7b/0x90
 do_syscall_64+0x3d/0x90
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 </TASK>

This can be prevented by forcing the inline data to be converted
and/or flushed beforehand.
This patch adds a call to ext4_convert_inline_data() just before
the BUG, which fixes the issue.

Link: https://syzkaller.appspot.com/bug?id=a1e89d09bbbcbd5c4cb45db230ee28c822953984
Reported-by: syzbot+bd13648a53ed6933ca49@...kaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk@...aro.org>
---
 fs/ext4/inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 84c0eb55071d..de2aa2e79052 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2717,6 +2717,10 @@ static int ext4_writepages(struct address_space *mapping,
 			ret = PTR_ERR(handle);
 			goto out_writepages;
 		}
+
+		if (ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA))
+			WARN_ON(ext4_convert_inline_data(inode));
+
 		BUG_ON(ext4_test_inode_state(inode,
 				EXT4_STATE_MAY_INLINE_DATA));
 		ext4_destroy_inline_data(handle, inode);
-- 
2.37.1