From 5643a977d0e2cca3877775f27a41df08e98d833a Mon Sep 17 00:00:00 2001 From: Siddhesh Poyarekar Date: Fri, 21 Jan 2022 23:32:56 +0530 Subject: 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 Reviewed-by: Adhemerval Zanella Signed-off-by: Qualys Security Advisory Signed-off-by: Siddhesh Poyarekar --- NEWS | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'NEWS') diff --git a/NEWS b/NEWS index 46b5a2d..e093778 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. -- cgit v1.1