linux-kernel - [PATCH] nilfs2: fix NULL pointer dereference in nilfs_segctor_prepare

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Date:   Tue, 8 Nov 2022 10:29:28 +0800
From:   Liu Shixin <liushixin2@...wei.com>
To:     Ryusuke Konishi <konishi.ryusuke@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-nilfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Liu Shixin <liushixin2@...wei.com>
Subject: [PATCH] nilfs2: fix NULL pointer dereference in nilfs_segctor_prepare_write()

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@...kaller.appspotmail.com
Fixes: 9ff05123e3bf ("nilfs2: segment constructor")
Signed-off-by: Liu Shixin <liushixin2@...wei.com>
---
 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