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@redhat.com>
Tested-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/romfs/internal.h b/fs/romfs/internal.h
index 06044a9..95217b8 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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)