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author | Siddhesh Poyarekar <siddhesh@sourceware.org> | 2022-01-19 09:43:26 +0530 |
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committer | Siddhesh Poyarekar <siddhesh@sourceware.org> | 2022-01-19 09:49:49 +0530 |
commit | 5af236968a7a5aff01d877ecb1f086bd743c571b (patch) | |
tree | 825b9a870c806783ba46e55fbbeba218a2690202 /features.h | |
parent | c9c20ec3b0e9831c1d0c47c9c51330c3e1685eae (diff) | |
download | glibc-siddhesh/realpath-and-getcwd.tar.gz glibc-siddhesh/realpath-and-getcwd.tar.xz glibc-siddhesh/realpath-and-getcwd.zip |
getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999) siddhesh/realpath-and-getcwd
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. Signed-off-by: Qualys Security Advisory <qsa@qualys.com> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Diffstat (limited to 'features.h')
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