ext4: avoid divide by zero fault when deleting corrupted inline directories

A specially crafted file system can trick empty_inline_dir() into
reading past the last valid entry in a inline directory, and then run
into the end of xattr marker. This will trigger a divide by zero
fault.  Fix this by using the size of the inline directory instead of
dir->i_size.

Also clean up error reporting in __ext4_check_dir_entry so that the
message is clearer and more understandable --- and avoids the division
by zero trap if the size passed in is zero.  (I'm not sure why we
coded it that way in the first place; printing offset % size is
actually more confusing and less useful.)

https://bugzilla.kernel.org/show_bug.cgi?id=200933

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Wen Xu <wen.xu@gatech.edu>
Cc: stable@vger.kernel.org

2 files changed, 12 insertions, 12 deletions

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index e2902d394f1b..f93f9881ec18 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -76,7 +76,7 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
         else if (unlikely(rlen < EXT4_DIR_REC_LEN(de->name_len)))
                 error_msg = "rec_len is too small for name_len";
         else if (unlikely(((char *) de - buf) + rlen > size))
-                error_msg = "directory entry across range";
+                error_msg = "directory entry overrun";
         else if (unlikely(le32_to_cpu(de->inode) >
                         le32_to_cpu(EXT4_SB(dir->i_sb)->s_es->s_inodes_count)))
                 error_msg = "inode out of bounds";
@@ -85,18 +85,16 @@ int __ext4_check_dir_entry(const char *function, unsigned int line,
 
         if (filp)
                 ext4_error_file(filp, function, line, bh->b_blocknr,
-                                "bad entry in directory: %s - offset=%u(%u), "
-                                "inode=%u, rec_len=%d, name_len=%d",
-                                error_msg, (unsigned) (offset % size),
-                                offset, le32_to_cpu(de->inode),
-                                rlen, de->name_len);
+                                "bad entry in directory: %s - offset=%u, "
+                                "inode=%u, rec_len=%d, name_len=%d, size=%d",
+                                error_msg, offset, le32_to_cpu(de->inode),
+                                rlen, de->name_len, size);
         else
                 ext4_error_inode(dir, function, line, bh->b_blocknr,
-                                "bad entry in directory: %s - offset=%u(%u), "
-                                "inode=%u, rec_len=%d, name_len=%d",
-                                error_msg, (unsigned) (offset % size),
-                                offset, le32_to_cpu(de->inode),
-                                rlen, de->name_len);
+                                "bad entry in directory: %s - offset=%u, "
+                                "inode=%u, rec_len=%d, name_len=%d, size=%d",
+                                 error_msg, offset, le32_to_cpu(de->inode),
+                                 rlen, de->name_len, size);
 
         return 1;
 }
diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 3543fe80a3c4..7b4736022761 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1753,6 +1753,7 @@ bool empty_inline_dir(struct inode *dir, int *has_inline_data)
 {
         int err, inline_size;
         struct ext4_iloc iloc;
+        size_t inline_len;
         void *inline_pos;
         unsigned int offset;
         struct ext4_dir_entry_2 *de;
@@ -1780,8 +1781,9 @@ bool empty_inline_dir(struct inode *dir, int *has_inline_data)
                 goto out;
         }
 
+        inline_len = ext4_get_inline_size(dir);
         offset = EXT4_INLINE_DOTDOT_SIZE;
-        while (offset < dir->i_size) {
+        while (offset < inline_len) {
                 de = ext4_get_inline_entry(dir, &iloc, offset,
                                            &inline_pos, &inline_size);
                 if (ext4_check_dir_entry(dir, NULL, de,