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Date: Thu, 23 Apr 2009 16:41:13 +0100
From: David Howells <dhowells@...hat.com>
To: torvalds@...l.org, akpm@...ux-foundation.org
Cc: dhowells@...hat.com, monstr@...str.eu, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] ROMFS: romfs_lookup() shouldn't be doing a partial name
comparison
romfs_lookup() should be using a routine akin to strcmp() on the backing store,
rather than one akin to strncmp(). If it uses the latter, it's liable to match
/bin/shutdown when looking up /bin/sh.
Signed-off-by: David Howells <dhowells@...hat.com>
Tested-by: Michal Simek <monstr@...str.eu>
---
fs/romfs/internal.h | 4 ++-
fs/romfs/storage.c | 67 +++++++++++++++++++++++++++++++++++++--------------
fs/romfs/super.c | 4 ++-
3 files changed, 53 insertions(+), 22 deletions(-)
diff --git a/fs/romfs/internal.h b/fs/romfs/internal.h
index 06044a9..95217b8 100644
--- a/fs/romfs/internal.h
+++ b/fs/romfs/internal.h
@@ -43,5 +43,5 @@ extern int romfs_dev_read(struct super_block *sb, unsigned long pos,
void *buf, size_t buflen);
extern ssize_t romfs_dev_strnlen(struct super_block *sb,
unsigned long pos, size_t maxlen);
-extern int romfs_dev_strncmp(struct super_block *sb, unsigned long pos,
- const char *str, size_t size);
+extern int romfs_dev_strcmp(struct super_block *sb, unsigned long pos,
+ const char *str, size_t size);
diff --git a/fs/romfs/storage.c b/fs/romfs/storage.c
index 7e3e1e1..66ce9dd 100644
--- a/fs/romfs/storage.c
+++ b/fs/romfs/storage.c
@@ -67,26 +67,35 @@ static ssize_t romfs_mtd_strnlen(struct super_block *sb,
* compare a string to one in a romfs image on MTD
* - return 1 if matched, 0 if differ, -ve if error
*/
-static int romfs_mtd_strncmp(struct super_block *sb, unsigned long pos,
- const char *str, size_t size)
+static int romfs_mtd_strcmp(struct super_block *sb, unsigned long pos,
+ const char *str, size_t size)
{
- u_char buf[16];
+ u_char buf[17];
size_t len, segment;
int ret;
- /* scan the string up to 16 bytes at a time */
+ /* scan the string up to 16 bytes at a time, and attempt to grab the
+ * trailing NUL whilst we're at it */
+ buf[0] = 0xff;
+
while (size > 0) {
- segment = min_t(size_t, size, 16);
+ segment = min_t(size_t, size + 1, 17);
ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
if (ret < 0)
return ret;
+ len--;
if (memcmp(buf, str, len) != 0)
return 0;
+ buf[0] = buf[len];
size -= len;
pos += len;
str += len;
}
+ /* check the trailing NUL was */
+ if (buf[0])
+ return 0;
+
return 1;
}
#endif /* CONFIG_ROMFS_ON_MTD */
@@ -154,28 +163,48 @@ static ssize_t romfs_blk_strnlen(struct super_block *sb,
* compare a string to one in a romfs image on a block device
* - return 1 if matched, 0 if differ, -ve if error
*/
-static int romfs_blk_strncmp(struct super_block *sb, unsigned long pos,
- const char *str, size_t size)
+static int romfs_blk_strcmp(struct super_block *sb, unsigned long pos,
+ const char *str, size_t size)
{
struct buffer_head *bh;
unsigned long offset;
size_t segment;
- bool x;
+ bool matched, terminated = false;
- /* scan the string up to 16 bytes at a time */
+ /* compare string up to a block at a time */
while (size > 0) {
offset = pos & (ROMBSIZE - 1);
segment = min_t(size_t, size, ROMBSIZE - offset);
bh = sb_bread(sb, pos >> ROMBSBITS);
if (!bh)
return -EIO;
- x = (memcmp(bh->b_data + offset, str, segment) != 0);
- brelse(bh);
- if (x)
- return 0;
+ matched = (memcmp(bh->b_data + offset, str, segment) == 0);
+
size -= segment;
pos += segment;
str += segment;
+ if (matched && size == 0 && offset + segment < ROMBSIZE) {
+ if (!bh->b_data[offset + segment])
+ terminated = true;
+ else
+ matched = false;
+ }
+ brelse(bh);
+ if (!matched)
+ return 0;
+ }
+
+ if (!terminated) {
+ /* the terminating NUL must be on the first byte of the next
+ * block */
+ BUG_ON((pos & (ROMBSIZE - 1)) != 0);
+ bh = sb_bread(sb, pos >> ROMBSBITS);
+ if (!bh)
+ return -EIO;
+ matched = !bh->b_data[0];
+ brelse(bh);
+ if (!matched)
+ return 0;
}
return 1;
@@ -234,10 +263,12 @@ ssize_t romfs_dev_strnlen(struct super_block *sb,
/*
* compare a string to one in romfs
+ * - the string to be compared to, str, may not be NUL-terminated; instead the
+ * string is of the specified size
* - return 1 if matched, 0 if differ, -ve if error
*/
-int romfs_dev_strncmp(struct super_block *sb, unsigned long pos,
- const char *str, size_t size)
+int romfs_dev_strcmp(struct super_block *sb, unsigned long pos,
+ const char *str, size_t size)
{
size_t limit;
@@ -246,16 +277,16 @@ int romfs_dev_strncmp(struct super_block *sb, unsigned long pos,
return -EIO;
if (size > ROMFS_MAXFN)
return -ENAMETOOLONG;
- if (size > limit - pos)
+ if (size + 1 > limit - pos)
return -EIO;
#ifdef CONFIG_ROMFS_ON_MTD
if (sb->s_mtd)
- return romfs_mtd_strncmp(sb, pos, str, size);
+ return romfs_mtd_strcmp(sb, pos, str, size);
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
if (sb->s_bdev)
- return romfs_blk_strncmp(sb, pos, str, size);
+ return romfs_blk_strcmp(sb, pos, str, size);
#endif
return -EIO;
}
diff --git a/fs/romfs/super.c b/fs/romfs/super.c
index 10ca7d9..c53b5ef 100644
--- a/fs/romfs/super.c
+++ b/fs/romfs/super.c
@@ -240,8 +240,8 @@ static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry,
goto error;
/* try to match the first 16 bytes of name */
- ret = romfs_dev_strncmp(dir->i_sb, offset + ROMFH_SIZE, name,
- len);
+ ret = romfs_dev_strcmp(dir->i_sb, offset + ROMFH_SIZE, name,
+ len);
if (ret < 0)
goto error;
if (ret == 1)
--
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