[PATCH AUTOSEL 6.10 33/34] ext4: sanity check for NULL pointer after ext4_force_shutdown

Sasha Levin
2024-07-28T15:45:14Z

From: Wojciech Gładysz <wojciech.gladysz@infogain.com>

[ Upstream commit 83f4414b8f84249d538905825b088ff3ae555652 ]

Test case: 2 threads write short inline data to a file.
In ext4_page_mkwrite the resulting inline data is converted.
Handling ext4_grp_locked_error with description "block bitmap
and bg descriptor inconsistent: X vs Y free clusters" calls
ext4_force_shutdown. The conversion clears
EXT4_STATE_MAY_INLINE_DATA but fails for
ext4_destroy_inline_data_nolock and ext4_mark_iloc_dirty due
to ext4_forced_shutdown. The restoration of inline data fails
for the same reason not setting EXT4_STATE_MAY_INLINE_DATA.
Without the flag set a regular process path in ext4_da_write_end
follows trying to dereference page folio private pointer that has
not been set. The fix calls early return with -EIO error shall the
pointer to private be NULL.

Sample crash report:

Unable to handle kernel paging request at virtual address dfff800000000004
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
Mem abort info:
ESR = 0x0000000096000005
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
Data abort info:
ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000004] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 20274 Comm: syz-executor185 Not tainted 6.9.0-rc7-syzkaller-gfda5695d692c #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __block_commit_write+0x64/0x2b0 fs/buffer.c:2167
lr : __block_commit_write+0x3c/0x2b0 fs/buffer.c:2160
sp : ffff8000a1957600
x29: ffff8000a1957610 x28: dfff800000000000 x27: ffff0000e30e34b0
x26: 0000000000000000 x25: dfff800000000000 x24: dfff800000000000
x23: fffffdffc397c9e0 x22: 0000000000000020 x21: 0000000000000020
x20: 0000000000000040 x19: fffffdffc397c9c0 x18: 1fffe000367bd196
x17: ffff80008eead000 x16: ffff80008ae89e3c x15: 00000000200000c0
x14: 1fffe0001cbe4e04 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000001 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : 0000000000000004 x7 : 0000000000000000 x6 : 0000000000000000
x5 : fffffdffc397c9c0 x4 : 0000000000000020 x3 : 0000000000000020
x2 : 0000000000000040 x1 : 0000000000000020 x0 : fffffdffc397c9c0
Call trace:
__block_commit_write+0x64/0x2b0 fs/buffer.c:2167
block_write_end+0xb4/0x104 fs/buffer.c:2253
ext4_da_do_write_end fs/ext4/inode.c:2955 [inline]
ext4_da_write_end+0x2c4/0xa40 fs/ext4/inode.c:3028
generic_perform_write+0x394/0x588 mm/filemap.c:3985
ext4_buffered_write_iter+0x2c0/0x4ec fs/ext4/file.c:299
ext4_file_write_iter+0x188/0x1780
call_write_iter include/linux/fs.h:2110 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x968/0xc3c fs/read_write.c:590
ksys_write+0x15c/0x26c fs/read_write.c:643
__do_sys_write fs/read_write.c:655 [inline]
__se_sys_write fs/read_write.c:652 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:652
__invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:133
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:152
el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712
el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
Code: 97f85911 f94002da 91008356 d343fec8 (38796908)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
0: 97f85911 bl 0xffffffffffe16444
4: f94002da ldr x26, [x22]
8: 91008356 add x22, x26, #0x20
c: d343fec8 lsr x8, x22, #3
* 10: 38796908 ldrb w8, [x8, x25] <-- trapping instruction

Reported-by: syzbot+18df508cf00a0598d9a6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=18df508cf00a0598d9a6
Link: https://lore.kernel.org/all/000000000000f19a1406109eb5c5@google.com/T/
Signed-off-by: Wojciech Gładysz <wojciech.gladysz@infogain.com>
Link: https://patch.msgid.link/20240703070112.10235-1-wojciech.gladysz@infogain.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/buffer.c | 2 ++
fs/ext4/inode.c | 5 +++++
2 files changed, 7 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 8c19e705b9c33..645f0387dfe1d 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2187,6 +2187,8 @@ static void __block_commit_write(struct folio *folio, size_t from, size_t to)
struct buffer_head *bh, *head;

bh = head = folio_buffers(folio);
+ if (!bh)
+ return;
blocksize = bh->b_size;

block_start = 0;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4bae9ccf5fe01..f14e77c4a6de8 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2945,6 +2945,11 @@ static int ext4_da_do_write_end(struct address_space *mapping,
bool disksize_changed = false;
loff_t new_i_size;

+ if (unlikely(!folio_buffers(folio))) {
+ folio_unlock(folio);
+ folio_put(folio);
+ return -EIO;
+ }
/*
* block_write_end() will mark the inode as dirty with I_DIRTY_PAGES
* flag, which all that's needed to trigger page writeback.
--
2.43.0