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squashfs: fix use of uninitialised variable in zlib & xz decompressors 

Fix potential use of uninitialised variable caused by recent
decompressor code optimisations.

In zlib_uncompress (zlib_wrapper.c) we have

	int zlib_err, zlib_init = 0;
	...
	do {
		...
			if (avail == 0) {
				offset = 0;
				put_bh(bh[k++]);
				continue;
			}
		...
		zlib_err = zlib_inflate(stream, Z_SYNC_FLUSH);
		...
	} while (zlib_err == Z_OK);

If continue is executed (avail == 0) then the while condition will be
evaluated testing zlib_err, which is uninitialised first time around the
loop.

Fix this by getting rid of the 'if (avail == 0)' condition test, this
edge condition should not be being handled in the decompressor code, and
instead handle it generically in the caller code.

Similarly for xz_wrapper.c.

Incidentally, on most architectures (bar Mips and Parisc), no
uninitialised variable warning is generated by gcc, this is because the
while condition test on continue is optimised out and not performed
(when executing continue zlib_err has not been changed since entering
the loop, and logically if the while condition was true previously, then
it's still true).

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
Reported-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Phillip Lougher 2011-01-25 15:07:34 -08:00 committed by Linus Torvalds
parent ac15ee691f
commit 3689456b4b
3 changed files with 8 additions and 12 deletions
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8
fs/squashfs/block.c
View File

@ -63,6 +63,14 @@ static struct buffer_head *get_block_length(struct super_block *sb,
*length = (unsigned char) bh->b_data[*offset] |
(unsigned char) bh->b_data[*offset + 1] << 8;
*offset += 2;
if (*offset == msblk->devblksize) {
put_bh(bh);
bh = sb_bread(sb, ++(*cur_index));
if (bh == NULL)
return NULL;
*offset = 0;
}
}
return bh;

6
fs/squashfs/xz_wrapper.c
View File

@ -95,12 +95,6 @@ static int squashfs_xz_uncompress(struct squashfs_sb_info *msblk, void **buffer,
if (!buffer_uptodate(bh[k]))
goto release_mutex;
if (avail == 0) {
offset = 0;
put_bh(bh[k++]);
continue;
}
stream->buf.in = bh[k]->b_data + offset;
stream->buf.in_size = avail;
stream->buf.in_pos = 0;

6
fs/squashfs/zlib_wrapper.c
View File

@ -82,12 +82,6 @@ static int zlib_uncompress(struct squashfs_sb_info *msblk, void **buffer,
if (!buffer_uptodate(bh[k]))
goto release_mutex;
if (avail == 0) {
offset = 0;
put_bh(bh[k++]);
continue;
}
stream->next_in = bh[k]->b_data + offset;
stream->avail_in = avail;
offset = 0;