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Harden create_temp_filename() (version 2)

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By hardening the create_temp_filename() function to check if the generated
filename exists and to create the temp file with only S_IRUSR|S_IWUSR bit
files set before calling the script, it should become even more difficult to
exploit such a scenario.

After a discussion on the mailing list, Fabian Knittel provided an enhanced
version of the inital patch which is added to this patch.

This patch also renames create_temp_filename() to create_temp_file(), as this
patch also creates the temporary file.  The function returns the filename of the
created file, or NULL on error.

Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
Signed-off-by: Fabian Knittel <fabian.knittel@avona.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
This commit is contained in:
David Sommerseth 2010-04-16 22:02:36 +02:00
parent 41104b4e23
commit 4e1cc5f6dd
2 changed files with 46 additions and 14 deletions
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56
misc.c
View File

@ -1165,25 +1165,57 @@ test_file (const char *filename)
/* create a temporary filename in directory */
const char *
create_temp_filename (const char *directory, const char *prefix, struct gc_arena *gc)
create_temp_file (const char *directory, const char *prefix, struct gc_arena *gc)
{
static unsigned int counter;
struct buffer fname = alloc_buf_gc (256, gc);
int fd;
const char *retfname = NULL;
unsigned int attempts = 0;
mutex_lock_static (L_CREATE_TEMP);
++counter;
mutex_unlock_static (L_CREATE_TEMP);
do
{
uint8_t rndbytes[16];
const char *rndstr;
{
uint8_t rndbytes[16];
const char *rndstr;
++attempts;
mutex_lock_static (L_CREATE_TEMP);
++counter;
mutex_unlock_static (L_CREATE_TEMP);
prng_bytes (rndbytes, sizeof (rndbytes));
rndstr = format_hex_ex (rndbytes, sizeof (rndbytes), 40, 0, NULL, gc);
buf_printf (&fname, PACKAGE "_%s_%s.tmp", prefix, rndstr);
}
prng_bytes (rndbytes, sizeof rndbytes);
rndstr = format_hex_ex (rndbytes, sizeof rndbytes, 40, 0, NULL, gc);
buf_printf (&fname, PACKAGE "_%s_%s.tmp", prefix, rndstr);
return gen_path (directory, BSTR (&fname), gc);
retfname = gen_path (directory, BSTR (&fname), gc);
if (!retfname)
{
msg (M_FATAL, "Failed to create temporary filename and path");
return NULL;
}
/* Atomically create the file. Errors out if the file already
exists. */
fd = open (retfname, O_CREAT | O_EXCL | O_WRONLY, S_IRUSR | S_IWUSR);
if (fd != -1)
{
close (fd);
return retfname;
}
else if (fd == -1 && errno != EEXIST)
{
/* Something else went wrong, no need to retry. */
struct gc_arena gcerr = gc_new ();
msg (M_FATAL, "Could not create temporary file '%s': %s",
retfname, strerror_ts (errno, &gcerr));
gc_free (&gcerr);
return NULL;
}
}
while (attempts < 6);
msg (M_FATAL, "Failed to create temporary file after %i attempts", attempts);
return NULL;
}
/*

4
misc.h
View File

@ -218,8 +218,8 @@ long int get_random(void);
/* return true if filename can be opened for read */
bool test_file (const char *filename);
/* create a temporary filename in directory */
const char *create_temp_filename (const char *directory, const char *prefix, struct gc_arena *gc);
/* create a temporary file in directory, returns the filename of the created file */
const char *create_temp_file (const char *directory, const char *prefix, struct gc_arena *gc);
/* put a directory and filename together */
const char *gen_path (const char *directory, const char *filename, struct gc_arena *gc);