udf: Check component length before reading it

Check that length specified in a component of a symlink fits in the
input buffer we are reading. Also properly ignore component length for
component types that do not use it. Otherwise we read memory after end
of buffer for corrupted udf image.

Reported-by: Carl Henrik Lunde <chlunde@ping.uio.no>
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/udf/symlink.c b/fs/udf/symlink.c
index 0f1b3a2654b9459a36c4df943f1f22a3bff070af..ac10ca939f267283ba0f64da9d4ec82de0eeeb61 100644 (file)
--- a/fs/udf/symlink.c
+++ b/fs/udf/symlink.c
@@ -42,14 +42,17 @@ static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
        tolen--;
        while (elen < fromlen) {
                pc = (struct pathComponent *)(from + elen);
+               elen += sizeof(struct pathComponent);
                switch (pc->componentType) {
                case 1:
                        /*
                         * Symlink points to some place which should be agreed
                         * upon between originator and receiver of the media. Ignore.
                         */
-                       if (pc->lengthComponentIdent > 0)
+                       if (pc->lengthComponentIdent > 0) {
+                               elen += pc->lengthComponentIdent;
                                break;
+                       }
                        /* Fall through */
                case 2:
                        if (tolen == 0)
@@ -74,6 +77,9 @@ static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
                        /* that would be . - just ignore */
                        break;
                case 5:
+                       elen += pc->lengthComponentIdent;
+                       if (elen > fromlen)
+                               return -EIO;
                        comp_len = udf_get_filename(sb, pc->componentIdent,
                                                    pc->lengthComponentIdent,
                                                    p, tolen);
@@ -85,7 +91,6 @@ static int udf_pc_to_char(struct super_block *sb, unsigned char *from,
                        tolen--;
                        break;
                }
-               elen += sizeof(struct pathComponent) + pc->lengthComponentIdent;
        }
        if (p > to + 1)
                p[-1] = '\0';