public inbox for glibc-cvs@sourceware.org
help / color / mirror / Atom feed
* [glibc/google/grte/v5-2.27/master] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
@ 2024-01-12 23:23 Pranav Kant
0 siblings, 0 replies; only message in thread
From: Pranav Kant @ 2024-01-12 23:23 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5643a977d0e2cca3877775f27a41df08e98d833a
commit 5643a977d0e2cca3877775f27a41df08e98d833a
Author: Siddhesh Poyarekar <siddhesh@sourceware.org>
Date: Fri Jan 21 23:32:56 2022 +0530
getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
Cherry-picked from 23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e in main branch.
Test included with this commit is not cherry-picked because it requires more
changes.
No valid path returned by getcwd would fit into 1 byte, so reject the
size early and return NULL with errno set to ERANGE. This change is
prompted by CVE-2021-3999, which describes a single byte buffer
underflow and overflow when all of the following conditions are met:
- The buffer size (i.e. the second argument of getcwd) is 1 byte
- The current working directory is too long
- '/' is also mounted on the current working directory
Sequence of events:
- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
because the linux kernel checks for name length before it checks
buffer size
- The code falls back to the generic getcwd in sysdeps/posix
- In the generic func, the buf[0] is set to '\0' on line 250
- this while loop on line 262 is bypassed:
while (!(thisdev == rootdev && thisino == rootino))
since the rootfs (/) is bind mounted onto the directory and the flow
goes on to line 449, where it puts a '/' in the byte before the
buffer.
- Finally on line 458, it moves 2 bytes (the underflowed byte and the
'\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
- buf is returned on line 469 and errno is not set.
This resolves BZ #28769.
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Diff:
---
NEWS | 6 ++++++
sysdeps/posix/getcwd.c | 8 ++++++++
2 files changed, 14 insertions(+)
diff --git a/NEWS b/NEWS
index 46b5a2d8d8..e0937786c8 100644
--- a/NEWS
+++ b/NEWS
@@ -28,6 +28,12 @@ Deprecated and removed features, and other changes affecting compatibility:
Security related changes:
+ CVE-2021-3999: Passing a buffer of size exactly 1 byte to the getcwd
+ function may result in an off-by-one buffer underflow and overflow
+ when the current working directory is longer than PATH_MAX and also
+ corresponds to the / directory through an unprivileged mount
+ namespace. Reported by Qualys.
+
CVE-2016-10739: The getaddrinfo function could successfully parse IPv4
addresses with arbitrary trailing characters, potentially leading to data
or command injection issues in applications.
diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
index b53433a2dc..154b9846a5 100644
--- a/sysdeps/posix/getcwd.c
+++ b/sysdeps/posix/getcwd.c
@@ -241,6 +241,14 @@ __getcwd (char *buf, size_t size)
char *path;
#ifndef NO_ALLOCATION
size_t allocated = size;
+
+ /* A size of 1 byte is never useful. */
+ if (allocated == 1)
+ {
+ __set_errno (ERANGE);
+ return NULL;
+ }
+
if (size == 0)
{
if (buf != NULL)
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2024-01-12 23:23 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-01-12 23:23 [glibc/google/grte/v5-2.27/master] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999) Pranav Kant
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).