[PATCH] jffs2: Fix use-after-free bug in jffs2_iget()'s error handling path

[Richard Weinberger]

On Thu, Sep 21, 2017 at 6:00 PM, Jake Daryll Obina <jake.obina at gmail.com> wrote:
> If jffs2_iget() fails for a newly-allocated inode, jffs2_do_clear_inode()
> can get called twice in the error handling path, the first call in
> jffs2_iget() itself and the second through iget_failed(). This can result
> to a use-after-free error in the second jffs2_do_clear_inode() call, such
> as shown by the oops below wherein the second jffs2_do_clear_inode() call
> was trying to free node fragments that were already freed in the first
> jffs2_do_clear_inode() call.
>
> [   78.178860] jffs2: error: (1904) jffs2_do_read_inode_internal: CRC failed for read_inode of inode 24 at physical location 0x1fc00c
> [   78.178914] Unable to handle kernel paging request at virtual address 6b6b6b6b6b6b6b7b
> [   78.185871] pgd = ffffffc03a567000
> [   78.188794] [6b6b6b6b6b6b6b7b] *pgd=0000000000000000, *pud=0000000000000000
> [   78.194968] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> ...
> [   78.513147] PC is at rb_first_postorder+0xc/0x28
> [   78.516503] LR is at jffs2_kill_fragtree+0x28/0x90 [jffs2]
> [   78.520672] pc : [<ffffff8008323d28>] lr : [<ffffff8000eb1cc8>] pstate: 60000105
> [   78.526757] sp : ffffff800cea38f0
> [   78.528753] x29: ffffff800cea38f0 x28: ffffffc01f3f8e80
> [   78.532754] x27: 0000000000000000 x26: ffffff800cea3c70
> [   78.536756] x25: 00000000dc67c8ae x24: ffffffc033d6945d
> [   78.540759] x23: ffffffc036811740 x22: ffffff800891a5b8
> [   78.544760] x21: 0000000000000000 x20: 0000000000000000
> [   78.548762] x19: ffffffc037d48910 x18: ffffff800891a588
> [   78.552764] x17: 0000000000000800 x16: 0000000000000c00
> [   78.556766] x15: 0000000000000010 x14: 6f2065646f6e695f
> [   78.560767] x13: 6461657220726f66 x12: 2064656c69616620
> [   78.564769] x11: 435243203a6c616e x10: 7265746e695f6564
> [   78.568771] x9 : 6f6e695f64616572 x8 : ffffffc037974038
> [   78.572774] x7 : bbbbbbbbbbbbbbbb x6 : 0000000000000008
> [   78.576775] x5 : 002f91d85bd44a2f x4 : 0000000000000000
> [   78.580777] x3 : 0000000000000000 x2 : 000000403755e000
> [   78.584779] x1 : 6b6b6b6b6b6b6b6b x0 : 6b6b6b6b6b6b6b6b
> ...
> [   79.038551] [<ffffff8008323d28>] rb_first_postorder+0xc/0x28
> [   79.042962] [<ffffff8000eb5578>] jffs2_do_clear_inode+0x88/0x100 [jffs2]
> [   79.048395] [<ffffff8000eb9ddc>] jffs2_evict_inode+0x3c/0x48 [jffs2]
> [   79.053443] [<ffffff8008201ca8>] evict+0xb0/0x168
> [   79.056835] [<ffffff8008202650>] iput+0x1c0/0x200
> [   79.060228] [<ffffff800820408c>] iget_failed+0x30/0x3c
> [   79.064097] [<ffffff8000eba0c0>] jffs2_iget+0x2d8/0x360 [jffs2]
> [   79.068740] [<ffffff8000eb0a60>] jffs2_lookup+0xe8/0x130 [jffs2]
> [   79.073434] [<ffffff80081f1a28>] lookup_slow+0x118/0x190
> [   79.077435] [<ffffff80081f4708>] walk_component+0xfc/0x28c
> [   79.081610] [<ffffff80081f4dd0>] path_lookupat+0x84/0x108
> [   79.085699] [<ffffff80081f5578>] filename_lookup+0x88/0x100
> [   79.089960] [<ffffff80081f572c>] user_path_at_empty+0x58/0x6c
> [   79.094396] [<ffffff80081ebe14>] vfs_statx+0xa4/0x114
> [   79.098138] [<ffffff80081ec44c>] SyS_newfstatat+0x58/0x98
> [   79.102227] [<ffffff800808354c>] __sys_trace_return+0x0/0x4
> [   79.106489] Code: d65f03c0 f9400001 b40000e1 aa0103e0 (f9400821)
>
> The jffs2_do_clear_inode() call in jffs2_iget() is unnecessary since
> iget_failed() will eventually call jffs2_do_clear_inode() if needed, so
> just remove it.
>
> Signed-off-by: Jake Daryll Obina <jake.obina at gmail.com>
> ---
>  fs/jffs2/fs.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/fs/jffs2/fs.c b/fs/jffs2/fs.c
> index e96c6b0..3c96f4b 100644
> --- a/fs/jffs2/fs.c
> +++ b/fs/jffs2/fs.c
> @@ -362,7 +362,6 @@ struct inode *jffs2_iget(struct super_block *sb, unsigned long ino)
>         ret = -EIO;
>  error:
>         mutex_unlock(&f->sem);
> -       jffs2_do_clear_inode(c, f);
>         iget_failed(inode);
>         return ERR_PTR(ret);
>  }
> --

Fixes: 5451f79f5f81 ("iget: stop JFFS2 from using iget() and read_inode()")
Reviewed-by: Richard Weinberger <richard at nod.at>

-- 
Thanks,
//richard