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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2022-01-21 23:32:56 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2022-01-24 11:00:17 +0530
commit23e0e8f5f1fb5ed150253d986ecccdc90c2dcd5e (patch)
tree4ce71226b6ce414b7c5a08d6406e5506f2b32442 /sysdeps/unix/sysv/linux/Makefile
parent6c2f050dbe11fb4ed0a401a5f25731f2aa53046b (diff)
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getcwd: Set errno to ERANGE for size == 1 (CVE-2021-3999)
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>
Diffstat (limited to 'sysdeps/unix/sysv/linux/Makefile')
-rw-r--r--sysdeps/unix/sysv/linux/Makefile7
1 files changed, 6 insertions, 1 deletions
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 85fc8cbf75..7ca9350c99 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -346,7 +346,12 @@ sysdep_routines += xstatconv internal_statvfs \
 
 sysdep_headers += bits/fcntl-linux.h
 
-tests += tst-fallocate tst-fallocate64 tst-o_path-locks
+tests += \
+  tst-fallocate \
+  tst-fallocate64 \
+  tst-getcwd-smallbuff \
+  tst-o_path-locks \
+# tests
 endif
 
 ifeq ($(subdir),elf)