Syzbot reported a NULL pointer dereference:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000168
Mem abort info:
ESR = 0x0000000096000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
Data abort info:
ISV = 0, ISS = 0x00000004
CM = 0, WnR = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=0000000108bcf000
[0000000000000168] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 3032 Comm: segctord Not tainted 6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022
pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : _compound_head include/linux/page-flags.h:253 [inline]
pc : lock_page+0x28/0x1e0 include/linux/pagemap.h:958
lr : lock_page+0x28/0x1e0 include/linux/pagemap.h:956
sp : ffff80001290bc00
x29: ffff80001290bc00 x28: ffff80001290bde0 x27: 000000000000001b
x26: fffffc000330d7c0 x25: ffff0000caa56d68 x24: ffff0000ca9fb1c0
x23: 0000000000000080 x22: ffff0000ca9fb130 x21: 0000000000000160
x20: ffff0000c91e10b8 x19: 0000000000000160 x18: 00000000000000c0
x17: ffff80000dd0b198 x16: ffff80000db49158 x15: ffff0000c3e63500
x14: 0000000000000000 x13: 00000000ffffffff x12: ffff0000c3e63500
x11: ff808000095d1a0c x10: 0000000000000000 x9 : 0000000000000000
x8 : 0000000000000000 x7 : ffff80000856806c x6 : 0000000000000000
x5 : 0000000000000080 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 0000000000000000 x1 : ffff80000cb431b1 x0 : 0000000000000000
Call trace:
lock_page+0x28/0x1e0 include/linux/pagemap.h:956
nilfs_segctor_prepare_write+0x6c/0x21c fs/nilfs2/segment.c:1658
nilfs_segctor_do_construct+0x9f4/0xee8 fs/nilfs2/segment.c:2068
nilfs_segctor_construct+0xa0/0x380 fs/nilfs2/segment.c:2375
nilfs_segctor_thread_construct fs/nilfs2/segment.c:2483 [inline]
nilfs_segctor_thread+0x180/0x660 fs/nilfs2/segment.c:2566
kthread+0x12c/0x158 kernel/kthread.c:376
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860
If didn't call nilfs_sufile_alloc() in nilfs_segctor_begin_construction(),
nilfs_sufile_header's sh_last_alloc is not updated. In such case, we will
add a bh in two segbuf->sb_segsum_buffers. And finally cause list error.
Reported-by: syzbot+77e4f005cb899d4268d1@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 9ff05123e3bf ("nilfs2: segment constructor")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
fs/nilfs2/segment.c | 1 +
fs/nilfs2/sufile.c | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index b4cebad21b48..7be632c15f91 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1371,6 +1371,7 @@ static int nilfs_segctor_extend_segments(struct nilfs_sc_info *sci,
sci->sc_segbuf_nblocks += segbuf->sb_rest_blocks;
/* allocate the next next full segment */
+ nextnextnum = segbuf->sb_segnum;
err = nilfs_sufile_alloc(sufile, &nextnextnum);
if (unlikely(err))
goto failed_segbuf;
diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
index 77ff8e95421f..853a8212114f 100644
--- a/fs/nilfs2/sufile.c
+++ b/fs/nilfs2/sufile.c
@@ -317,7 +317,7 @@ int nilfs_sufile_alloc(struct inode *sufile, __u64 *segnump)
goto out_sem;
kaddr = kmap_atomic(header_bh->b_page);
header = kaddr + bh_offset(header_bh);
- last_alloc = le64_to_cpu(header->sh_last_alloc);
+ last_alloc = max(le64_to_cpu(header->sh_last_alloc), *segnump);
kunmap_atomic(kaddr);
nsegments = nilfs_sufile_get_nsegments(sufile);
--
2.25.1
