diff options
Diffstat (limited to 'aports/busybox/0014-ash-fix-use-after-free-in-bash-pattern-substitution.patch')
| -rw-r--r-- | aports/busybox/0014-ash-fix-use-after-free-in-bash-pattern-substitution.patch | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/aports/busybox/0014-ash-fix-use-after-free-in-bash-pattern-substitution.patch b/aports/busybox/0014-ash-fix-use-after-free-in-bash-pattern-substitution.patch new file mode 100644 index 0000000..6ff2b82 --- /dev/null +++ b/aports/busybox/0014-ash-fix-use-after-free-in-bash-pattern-substitution.patch @@ -0,0 +1,81 @@ +From 103728181bfd9a60537166d036e5baca7b67cc1f Mon Sep 17 00:00:00 2001 +From: =?UTF-8?q?S=C3=B6ren=20Tempel?= <soeren@soeren-tempel.net> +Date: Sat, 29 Jan 2022 06:11:12 +0100 +Subject: [PATCH] ash: fix use-after-free in bash pattern substitution +MIME-Version: 1.0 +Content-Type: text/plain; charset=UTF-8 +Content-Transfer-Encoding: 8bit + +At Alpine Linux downstream, we were made aware of a segmentation fault +occurring during string replacement in BusyBox ash [0]. Further +debugging revealed that the segmentation fault occurs due to a +use-after-free in BusyBox's bash pattern substitution implementation. +Specially, the problem is that the repl variable (pointing to the +replacement string) points to a value in the stack string. However, when +accessing the repl pointer in Line 7350 it is possible that the stack +has been moved since the last repl assignment due to the STPUTC +invocations in Line 7317 and 7321 (since STPUTC may grow the stack via +realloc(3)). + +For this reason, the code in Line 7350 may access an unmapped memory +region and therefore causes a segmentation fault if prior STPUTC +invocations moved the stack via realloc(3). The valgrind output +for this edge case looks as follows: + + Invalid read of size 1 + at 0x15D8DD: subevalvar (ash.c:7350) + by 0x15DC43: evalvar (ash.c:7666) + by 0x15B717: argstr (ash.c:6893) + by 0x15BAEC: expandarg (ash.c:8090) + by 0x15F4CC: evalcommand (ash.c:10429) + by 0x15B26C: evaltree (ash.c:9365) + by 0x15E4FC: cmdloop (ash.c:13569) + by 0x15FD8B: ash_main (ash.c:14748) + by 0x115BF2: run_applet_no_and_exit (appletlib.c:967) + by 0x115F16: run_applet_and_exit (appletlib.c:986) + by 0x115EF9: busybox_main (appletlib.c:917) + by 0x115EF9: run_applet_and_exit (appletlib.c:979) + by 0x115F8F: main (appletlib.c:1126) + Address 0x48b8646 is 2,054 bytes inside a block of size 4,776 free'd + at 0x48A6FC9: realloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so) + by 0x116E86: xrealloc (xfuncs_printf.c:61) + by 0x1565DB: growstackblock (ash.c:1736) + by 0x156EF7: growstackstr (ash.c:1775) + by 0x156F1A: _STPUTC (ash.c:1816) + by 0x15D843: subevalvar (ash.c:7317) + by 0x15DC43: evalvar (ash.c:7666) + by 0x15B717: argstr (ash.c:6893) + by 0x15BAEC: expandarg (ash.c:8090) + by 0x15F4CC: evalcommand (ash.c:10429) + by 0x15B26C: evaltree (ash.c:9365) + by 0x15E4FC: cmdloop (ash.c:13569) + +A testcase for reproducing this edge case is provided in the downstream +bug report [1]. This commit fixes the issue by reconstructing the repl +pointer relative to stackblock() via strloc and slash_pos. + +[0]: https://gitlab.alpinelinux.org/alpine/aports/-/issues/13469 +[1]: https://gitlab.alpinelinux.org/alpine/aports/-/issues/13469#note_210530 + +Signed-off-by: Sören Tempel <soeren@soeren-tempel.net> +--- + shell/ash.c | 6 ++++++ + 1 file changed, 6 insertions(+) + +diff --git a/shell/ash.c b/shell/ash.c +index 55df54bd0..24f9a8270 100644 +--- a/shell/ash.c ++++ b/shell/ash.c +@@ -7346,6 +7346,12 @@ subevalvar(char *start, char *str, int strloc, + idx = loc; + } + ++ // The STPUTC invocations above may resize and move the ++ // stack via realloc(3). Since repl is a pointer into the ++ // stack, we need to reconstruct it relative to stackblock(). ++ if (slash_pos >= 0) ++ repl = (char *)stackblock() + strloc + slash_pos + 1; ++ + //bb_error_msg("repl:'%s'", repl); + for (loc = (char*)repl; *loc; loc++) { + char *restart_detect = stackblock(); |