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* [PATCH] gdb/source.c: Fix undefined behaviour dereferencing empty string
@ 2022-09-15 18:31 Magne Hov
  2022-09-20 19:07 ` Tom Tromey
  2022-09-21 14:58 ` [PATCH v2] " Magne Hov
  0 siblings, 2 replies; 7+ messages in thread
From: Magne Hov @ 2022-09-15 18:31 UTC (permalink / raw)
  To: gdb-patches

When a source file's dirname is solely made up of directory separators
we end up trying to dereference the last character of an empty string
with std::string::back, which results in undefined behaviour. A typical
use case where this can happen is when the root directory "/" is used as
a compilation directory.

With libstdc++.so.6.0.28 we get no out-of-bounds checks and the byte
preceding the storage of the empty string is returned. The character
value of this byte depends on heap implementation and usage, but when
this byte happens to hold the value of the directory separator character
we go on to call std::string::pop_back on the empty string which results
in an out_of_range exception which terminates GDB.

Fix this by checking for the empty string.

The testsuite has been run before and after the change and no
regressions were found.
---
 gdb/source.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/source.c b/gdb/source.c
index 3f498d552c4..9d69052c4f1 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -1149,7 +1149,7 @@ find_and_open_source (const char *filename,
       std::string cdir_filename (dirname);
 
       /* Remove any trailing directory separators.  */
-      while (IS_DIR_SEPARATOR (cdir_filename.back ()))
+      while (!cdir_filename.empty () && IS_DIR_SEPARATOR (cdir_filename.back ()))
 	cdir_filename.pop_back ();
 
       /* Add our own directory separator.  */
-- 
2.25.1


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2022-09-24  8:58 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-09-15 18:31 [PATCH] gdb/source.c: Fix undefined behaviour dereferencing empty string Magne Hov
2022-09-20 19:07 ` Tom Tromey
2022-09-21 14:51   ` Magne Hov
2022-09-21 14:58 ` [PATCH v2] " Magne Hov
2022-09-21 15:52   ` Simon Marchi
2022-09-22 13:11     ` Magne Hov
2022-09-24  8:58   ` Magne Hov

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