71 lines
2.2 KiB
Diff
71 lines
2.2 KiB
Diff
From 472e799a5f2102bc0c3206dbd5a801765fceb39c Mon Sep 17 00:00:00 2001
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From: Siddhesh Poyarekar <siddhesh@sourceware.org>
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Date: Fri, 21 Jan 2022 23:32:56 +0530
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Subject: [PATCH] getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
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No valid path returned by getcwd would fit into 1 byte, so reject the
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size early and return NULL with errno set to ERANGE. This change is
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prompted by CVE-2021-3999, which describes a single byte buffer
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underflow and overflow when all of the following conditions are met:
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- The buffer size (i.e. the second argument of getcwd) is 1 byte
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- The current working directory is too long
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- '/' is also mounted on the current working directory
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Sequence of events:
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- In sysdeps/unix/sysv/linux/getcwd.c, the syscall returns ENAMETOOLONG
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because the linux kernel checks for name length before it checks
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buffer size
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- The code falls back to the generic getcwd in sysdeps/posix
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- In the generic func, the buf[0] is set to '\0' on line 269
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- this while loop on line 282 is bypassed:
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while (!(thisdev == rootdev && thisino == rootino))
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since the rootfs (/) is bind mounted onto the directory and the flow
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goes on to line 492, where it puts a '/' in the byte before the
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buffer.
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- Finally on line 500, it moves 2 bytes (the underflowed byte and the
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'\0') to the buf[0] and buf[1], resulting in a 1 byte buffer overflow.
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- buf is returned on line 514 and errno is not set.
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This resolves BZ #28769.
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Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>
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Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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Signed-off-by: Qualys Security Advisory <qsa@qualys.com>
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Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
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(cherry picked from commit 23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e)
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---
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sysdeps/posix/getcwd.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/sysdeps/posix/getcwd.c b/sysdeps/posix/getcwd.c
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index b53433a2..e3c1d77c 100644
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--- a/sysdeps/posix/getcwd.c
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+++ b/sysdeps/posix/getcwd.c
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@@ -239,6 +239,14 @@ __getcwd (char *buf, size_t size)
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int fd = AT_FDCWD;
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char *path;
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+
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+ /* A size of 1 byte is never useful. */
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+ if (size == 1)
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+ {
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+ __set_errno (ERANGE);
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+ return NULL;
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+ }
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+
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#ifndef NO_ALLOCATION
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size_t allocated = size;
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if (size == 0)
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--
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2.27.0
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