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Btrfs: Avoid accessing unmapped kernel address

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When decompressing a chunk of data, we'll copy the data out to
a working buffer if the data is stored in more than one page,
otherwise we'll use the mapped page directly to avoid memory
copy.

In the latter case, we'll end up accessing the kernel address
after we've unmapped the page in a corner case.

Reported-by: Juan Francisco Cantero Hurtado <iam@juanfra.info>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Li Zefan 2011-02-16 06:06:41 +00:00 committed by Chris Mason
parent b4dc2b8c69
commit ca9b688c1c
1 changed files with 14 additions and 7 deletions
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21
fs/btrfs/lzo.c
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@ -280,6 +280,7 @@ static int lzo_decompress_biovec(struct list_head *ws,
unsigned long tot_out;
unsigned long tot_len;
char *buf;
bool may_late_unmap, need_unmap;
data_in = kmap(pages_in[0]);
tot_len = read_compress_length(data_in);
@ -300,11 +301,13 @@ static int lzo_decompress_biovec(struct list_head *ws,
tot_in += in_len;
working_bytes = in_len;
may_late_unmap = need_unmap = false;
/* fast path: avoid using the working buffer */
if (in_page_bytes_left >= in_len) {
buf = data_in + in_offset;
bytes = in_len;
may_late_unmap = true;
goto cont;
}
@ -329,14 +332,17 @@ cont:
if (working_bytes == 0 && tot_in >= tot_len)
break;
kunmap(pages_in[page_in_index]);
page_in_index++;
if (page_in_index >= total_pages_in) {
if (page_in_index + 1 >= total_pages_in) {
ret = -1;
data_in = NULL;
goto done;
}
data_in = kmap(pages_in[page_in_index]);
if (may_late_unmap)
need_unmap = true;
else
kunmap(pages_in[page_in_index]);
data_in = kmap(pages_in[++page_in_index]);
in_page_bytes_left = PAGE_CACHE_SIZE;
in_offset = 0;
@ -346,6 +352,8 @@ cont:
out_len = lzo1x_worst_compress(PAGE_CACHE_SIZE);
ret = lzo1x_decompress_safe(buf, in_len, workspace->buf,
&out_len);
if (need_unmap)
kunmap(pages_in[page_in_index - 1]);
if (ret != LZO_E_OK) {
printk(KERN_WARNING "btrfs decompress failed\n");
ret = -1;
@ -363,8 +371,7 @@ cont:
break;
}
done:
if (data_in)
kunmap(pages_in[page_in_index]);
kunmap(pages_in[page_in_index]);
return ret;
}