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Date: Thu, 16 Nov 2023 06:58:39 -0800
From: Kees Cook <keescook@...omium.org>
To: Ronald Monthero <debug.penguin32@...il.com>
Cc: al@...rsen.net, gustavoars@...nel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH] qnx4: fix to avoid panic due to buffer overflow
On Thu, Nov 16, 2023 at 06:29:59AM -0800, Kees Cook wrote:
> On Sun, Nov 12, 2023 at 07:53:53PM +1000, Ronald Monthero wrote:
> > qnx4 dir name length can vary to be of maximum size
> > QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> > 'link info' entry is stored and the status byte is set.
> > So to avoid buffer overflow check di_fname length
> > fetched from (struct qnx4_inode_entry *)
> > before use in strlen to avoid buffer overflow.
> >
> > panic context
> > [ 4849.636861] detected buffer overflow in strlen
> > [ 4849.636897] ------------[ cut here ]------------
> > [ 4849.636902] kernel BUG at lib/string.c:1165!
> > [ 4849.636917] invalid opcode: 0000 [#2] SMP PTI
> > ..
> > [ 4849.637047] Call Trace:
> > [ 4849.637053] <TASK>
> > [ 4849.637059] ? show_trace_log_lvl+0x1d6/0x2ea
> > [ 4849.637075] ? show_trace_log_lvl+0x1d6/0x2ea
> > [ 4849.637095] ? qnx4_find_entry.cold+0xc/0x18 [qnx4]
> > [ 4849.637111] ? show_regs.part.0+0x23/0x29
> > [ 4849.637123] ? __die_body.cold+0x8/0xd
> > [ 4849.637135] ? __die+0x2b/0x37
> > [ 4849.637147] ? die+0x30/0x60
> > [ 4849.637161] ? do_trap+0xbe/0x100
> > [ 4849.637171] ? do_error_trap+0x6f/0xb0
> > [ 4849.637180] ? fortify_panic+0x13/0x15
> > [ 4849.637192] ? exc_invalid_op+0x53/0x70
> > [ 4849.637203] ? fortify_panic+0x13/0x15
> > [ 4849.637215] ? asm_exc_invalid_op+0x1b/0x20
> > [ 4849.637228] ? fortify_panic+0x13/0x15
> > [ 4849.637240] ? fortify_panic+0x13/0x15
> > [ 4849.637251] qnx4_find_entry.cold+0xc/0x18 [qnx4]
> > [ 4849.637264] qnx4_lookup+0x3c/0xa0 [qnx4]
> > [ 4849.637275] __lookup_slow+0x85/0x150
> > [ 4849.637291] walk_component+0x145/0x1c0
> > [ 4849.637304] ? path_init+0x2c0/0x3f0
> > [ 4849.637316] path_lookupat+0x6e/0x1c0
> > [ 4849.637330] filename_lookup+0xcf/0x1d0
> > [ 4849.637341] ? __check_object_size+0x1d/0x30
> > [ 4849.637354] ? strncpy_from_user+0x44/0x150
> > [ 4849.637365] ? getname_flags.part.0+0x4c/0x1b0
> > [ 4849.637375] user_path_at_empty+0x3f/0x60
> > [ 4849.637383] vfs_statx+0x7a/0x130
> > [ 4849.637393] do_statx+0x45/0x80
> > ..
> >
> > Signed-off-by: Ronald Monthero <debug.penguin32@...il.com>
> > ---
> > fs/qnx4/namei.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > index 8d72221735d7..825b891a52b3 100644
> > --- a/fs/qnx4/namei.c
> > +++ b/fs/qnx4/namei.c
> > @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
> > } else {
> > namelen = QNX4_SHORT_NAME_MAX;
> > }
> > +
> > + /** qnx4 dir name length can vary, check the di_fname
> > + * fetched from (struct qnx4_inode_entry *) before use in
> > + * strlen to avoid panic due to buffer overflow"
> > + */
>
> Style nit: this comment should start with just "/*" alone, like:
>
> /*
> * qnx4 dir name ...
>
> > + if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> > + return -ENAMETOOLONG;
> > thislen = strlen( de->di_fname );
>
> de->di_fname is:
>
> struct qnx4_inode_entry {
> char di_fname[QNX4_SHORT_NAME_MAX];
> ...
>
> #define QNX4_SHORT_NAME_MAX 16
> #define QNX4_NAME_MAX 48
>
> It's always going to have a max of QNX4_SHORT_NAME_MAX. Is any of this
> code correct if namelen ends up being QNX4_NAME_MAX? It'll be reading
> past the end of di_fname.
>
> Is bh->b_data actually struct qnx4_inode_entry ?
Ah-ha, it looks like it's _not_:
if (!(bh = qnx4_find_entry(len, dir, name, &de, &ino)))
goto out;
/* The entry is linked, let's get the real info */
if ((de->di_status & QNX4_FILE_LINK) == QNX4_FILE_LINK) {
lnk = (struct qnx4_link_info *) de;
It seems that entries may be either struct qnx4_inode_entry or struct
qnx4_link_info but it's not captured in a union.
This needs to be fixed by not lying to the compiler about what is there.
How about this?
diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
index 8d72221735d7..3cd20065bcfa 100644
--- a/fs/qnx4/namei.c
+++ b/fs/qnx4/namei.c
@@ -26,31 +26,39 @@
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_dir_entry *de;
+ char *entry_fname;
+ int entry_len, entry_max_len;
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_dir_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) {
+
+ switch (de->inode.di_status) {
+ case QNX4_FILE_LINK:
+ entry_fname = de->link.dl_fname;
+ entry_max_len = sizeof(de->link.dl_fname);
+ break;
+ case QNX4_FILE_USED:
+ entry_fname = de->inode.di_fname;
+ entry_max_len = sizeof(de->inode.di_fname);
+ break;
+ default:
return 0;
}
- if (strncmp(name, de->di_fname, len) == 0) {
- if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) != 0) {
- return 1;
- }
- }
+
+ /* Directory entry may not be %NUL-terminated. */
+ entry_len = strnlen(entry_fname, entry_max_len);
+
+ if (len != entry_len)
+ return 0;
+
+ if (strncmp(name, entry_fname, len) == 0)
+ return 1;
+
return 0;
}
diff --git a/include/uapi/linux/qnx4_fs.h b/include/uapi/linux/qnx4_fs.h
index 31487325d265..e033dbe1e009 100644
--- a/include/uapi/linux/qnx4_fs.h
+++ b/include/uapi/linux/qnx4_fs.h
@@ -68,6 +68,13 @@ struct qnx4_link_info {
__u8 dl_status;
};
+union qnx4_dir_entry {
+ struct qnx4_inode_entry inode;
+ struct qnx4_link_info link;
+};
+_Static_assert(offsetof(struct qnx4_inode_entry, di_status) ==
+ offsetof(struct qnx4_link_info, dl_status));
+
struct qnx4_xblk {
__le32 xblk_next_xblk;
__le32 xblk_prev_xblk;
--
Kees Cook
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