Fix use-after-free in glob when expanding ~user (bug 25414)

Message ID mvmmu9e1pyd.fsf@suse.de
State New
Headers show
Series
  • Fix use-after-free in glob when expanding ~user (bug 25414)
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Commit Message

Andreas Schwab Feb. 19, 2020, 4:50 p.m.
The value of `end_name' points into the value of `dirname', thus don't
deallocate the latter before the last use of the former.
---
 posix/glob.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

-- 
2.25.1


-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Comments

Paul Eggert Feb. 19, 2020, 8:40 p.m. | #1
On 2/19/20 8:50 AM, Andreas Schwab wrote:

> +		int use_alloca = glob_use_alloca (alloca_used,

> +						  home_len + rest_len + 1);


I suggest using 'bool' instead of 'int' here, since the value is boolean 
and glob_use_alloca returns 'bool'. Although some of the nearby local 
vars use 'int' to represent booleans, surely this is because the code 
predates 'bool'; for new code it's better to use 'bool' for booleans.

Otherwise, looks good; thanks.

Patch

diff --git a/posix/glob.c b/posix/glob.c
index cba9cd1819..0708ed5ee4 100644
--- a/posix/glob.c
+++ b/posix/glob.c
@@ -827,31 +827,32 @@  __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
 	      {
 		size_t home_len = strlen (p->pw_dir);
 		size_t rest_len = end_name == NULL ? 0 : strlen (end_name);
-		char *d;
+		char *d, *newp;
+		int use_alloca = glob_use_alloca (alloca_used,
+						  home_len + rest_len + 1);
 
-		if (__glibc_unlikely (malloc_dirname))
-		  free (dirname);
-		malloc_dirname = 0;
-
-		if (glob_use_alloca (alloca_used, home_len + rest_len + 1))
-		  dirname = alloca_account (home_len + rest_len + 1,
-					    alloca_used);
+		if (use_alloca)
+		  newp = alloca_account (home_len + rest_len + 1, alloca_used);
 		else
 		  {
-		    dirname = malloc (home_len + rest_len + 1);
-		    if (dirname == NULL)
+		    newp = malloc (home_len + rest_len + 1);
+		    if (newp == NULL)
 		      {
 			scratch_buffer_free (&pwtmpbuf);
 			retval = GLOB_NOSPACE;
 			goto out;
 		      }
-		    malloc_dirname = 1;
 		  }
-		d = mempcpy (dirname, p->pw_dir, home_len);
+		d = mempcpy (newp, p->pw_dir, home_len);
 		if (end_name != NULL)
 		  d = mempcpy (d, end_name, rest_len);
 		*d = '\0';
 
+		if (__glibc_unlikely (malloc_dirname))
+		  free (dirname);
+		dirname = newp;
+		malloc_dirname = !use_alloca;
+
 		dirlen = home_len + rest_len;
 		dirname_modified = 1;
 	      }