[PATCH v2 2/2] qnx4: Use get_directory_fname() in qnx4_match()

Kees Cook
2023-11-30T20:51:31Z

Use the new common directory entry name accessor helper to avoid
confusing the compiler about over-running the file name buffer. Avoids
false positive buffer overflow warning:

[ 4849.636861] detected buffer overflow in strlen
[ 4849.636897] ------------[ cut here ]------------
[ 4849.636902] kernel BUG at lib/string.c:1165!
...
[ 4849.637047] Call Trace:
...
[ 4849.637251] qnx4_find_entry.cold+0xc/0x18 [qnx4]
[ 4849.637264] qnx4_lookup+0x3c/0xa0 [qnx4]

Cc: Anders Larsen <al@alarsen.net>
Reported-by: Ronald Monthero <debug.penguin32@gmail.com>
Closes: https://lore.kernel.org/lkml/20231112095353.579855-1-debug.penguin32@gmail.com/
Link: https://lore.kernel.org/r/20231118033225.2181299-2-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/qnx4/namei.c | 29 +++++++++++------------------
1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
index 8d72221735d7..bb8db6550ca5 100644
--- a/fs/qnx4/namei.c
+++ b/fs/qnx4/namei.c
@@ -26,31 +26,24 @@
static int qnx4_match(int len, const char *name,
struct buffer_head *bh, unsigned long *offset)
{
- struct qnx4_inode_entry *de;
- int namelen, thislen;
+ union qnx4_directory_entry *de;
+ const char *fname;
+ int fnamelen;

if (bh == NULL) {
printk(KERN_WARNING "qnx4: matching unassigned buffer !\n");
return 0;
}
- de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
+ de = (union qnx4_directory_entry *) (bh->b_data + *offset);
*offset += QNX4_DIR_ENTRY_SIZE;
- if ((de->di_status & QNX4_FILE_LINK) != 0) {
- namelen = QNX4_NAME_MAX;
- } else {
- namelen = QNX4_SHORT_NAME_MAX;
- }
- thislen = strlen( de->di_fname );
- if ( thislen > namelen )
- thislen = namelen;
- if (len != thislen) {
+
+ fname = get_entry_fname(de, &fnamelen);
+ if (!fname || len != fnamelen)
return 0;
- }
- if (strncmp(name, de->di_fname, len) == 0) {
- if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) != 0) {
- return 1;
- }
- }
+
+ if (strncmp(name, fname, len) == 0)
+ return 1;
+
return 0;
}

--
2.34.1