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Old 06-18-2012, 07:31 AM
Masatake YAMATO
 
Default Fixing double brelse'ing bh allocated in gfs2_meta_read when EIO occurs

This patch fixes buffer_head double free in following code path:

gfs2_block_map
=> gfs2_meta_inode_buffer
=> gfs2_meta_indirect_buffer
=> gfs2_meta_read
=> release_metapath


gfs2_block_map calls gfs2_meta_inode_buffer with &mp.mp_bh[0]
as an argument. mp.mp_bh are filled with zero at the beginning
of gfs2_block_map.

If gfs2_meta_inode_buffer returns non-zero value, gfs2_block_map
calls release_metapath to free buffers chained to mp.mp_bh.
release_metapath checks each slot of mp.mp_bh[i] and
free(with brelse) unless the slot is filled with NULL.


&mp.mp_bh[0] passed to gfs2_meta_inode_buffer is filled at
gfs2_meta_read. gfs2_meta_read is filled a buffer allocated with
gfs2_getbuf even if EIO occurs. When EIO occurs, the allocated buffer
is brelse'ed though the pointer(wrong poiner) points the brelse'ed is
passed back to caller via an argument bhp.

gfs2_meta_indirect_buffer, the caller also pass the wrong pointer
to its caller with EIO. Finally gfs2_block_map gets both EIO and
&mp.mp_bh[0] filled with the wrong pointer. release_metapath
calls brelse again on the wrong pointer.

Signed-off-by: Masatake YAMATO<yamato@redhat.com>

diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 6c1e5d1..3a56c8d 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -213,8 +213,10 @@ int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
struct gfs2_sbd *sdp = gl->gl_sbd;
struct buffer_head *bh;

- if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
+ if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
+ *bhp = NULL;
return -EIO;
+ }

*bhp = bh = gfs2_getbuf(gl, blkno, CREATE);

@@ -235,6 +237,7 @@ int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
if (tr && tr->tr_touched)
gfs2_io_error_bh(sdp, bh);
brelse(bh);
+ *bhp = NULL;
return -EIO;
}
 
Old 06-28-2012, 03:02 PM
Steven Whitehouse
 
Default Fixing double brelse'ing bh allocated in gfs2_meta_read when EIO occurs

Hi,

Many thanks for the patch. I've added it to the -nmw git tree. Sorry for
the delay, just getting back up to speed after my holiday,

Steve.

On Mon, 2012-06-18 at 16:31 +0900, Masatake YAMATO wrote:
> This patch fixes buffer_head double free in following code path:
>
> gfs2_block_map
> => gfs2_meta_inode_buffer
> => gfs2_meta_indirect_buffer
> => gfs2_meta_read
> => release_metapath
>
>
> gfs2_block_map calls gfs2_meta_inode_buffer with &mp.mp_bh[0]
> as an argument. mp.mp_bh are filled with zero at the beginning
> of gfs2_block_map.
>
> If gfs2_meta_inode_buffer returns non-zero value, gfs2_block_map
> calls release_metapath to free buffers chained to mp.mp_bh.
> release_metapath checks each slot of mp.mp_bh[i] and
> free(with brelse) unless the slot is filled with NULL.
>
>
> &mp.mp_bh[0] passed to gfs2_meta_inode_buffer is filled at
> gfs2_meta_read. gfs2_meta_read is filled a buffer allocated with
> gfs2_getbuf even if EIO occurs. When EIO occurs, the allocated buffer
> is brelse'ed though the pointer(wrong poiner) points the brelse'ed is
> passed back to caller via an argument bhp.
>
> gfs2_meta_indirect_buffer, the caller also pass the wrong pointer
> to its caller with EIO. Finally gfs2_block_map gets both EIO and
> &mp.mp_bh[0] filled with the wrong pointer. release_metapath
> calls brelse again on the wrong pointer.
>
> Signed-off-by: Masatake YAMATO<yamato@redhat.com>
>
> diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
> index 6c1e5d1..3a56c8d 100644
> --- a/fs/gfs2/meta_io.c
> +++ b/fs/gfs2/meta_io.c
> @@ -213,8 +213,10 @@ int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
> struct gfs2_sbd *sdp = gl->gl_sbd;
> struct buffer_head *bh;
>
> - if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
> + if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags))) {
> + *bhp = NULL;
> return -EIO;
> + }
>
> *bhp = bh = gfs2_getbuf(gl, blkno, CREATE);
>
> @@ -235,6 +237,7 @@ int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
> if (tr && tr->tr_touched)
> gfs2_io_error_bh(sdp, bh);
> brelse(bh);
> + *bhp = NULL;
> return -EIO;
> }
>
>
 

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