clone: plug a miniscule leak
PATCH 1/1 clone: plug a miniscule leak
The remote_name variable is first assigned a copy of the value of the "clone.defaultremotename" configuration variable and then by the value of the "--origin" command line option. The former is prepared to see multiple instances of the variable by freeing the current value of the variable before a copy of the newly discovered value gets assigned to it. The latter blindly assigned a copy of the new value to it, thereby leaking the value read from the configuration.
---
This was discovered by a recently removed bogus coccinelle rewrite rule---if you apply an incorrect change suggested by the bogus rewrite rule to unconditionally assign to remote_name a copy of option_origin, or NULL, the value read from the configuration would be lost and never be used, thereby breaking a test to ensure the configuration is used, instead of the default remote nickname "origin".
Perhaps a Coccinelle rule like this might have caught similar leaks:
@@
expression E;
expression V;
@@
- if (E)
- V = xstrdup(E);
+ if (E) {
+ free(V);
+ V = xstrdup(E);
+ }
The fact that the result of xstrdup() is assigned to V is that V is meant to hold a pointer to an allocated piece of memory.
With the preimage of the above semantic patch, it is reasonable to expect that V may be initialized to NULL or may be holding a pointer to a piece of allocated memory when the control reaches here, because otherwise, V will be either need to be freed (when E was not NULL, in which case we assigned the result of xstrdup() to it) or V has garbage that cannot be freed later.
builtin/clone.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
builtin/clone.c +3 -1
@@ -1106,8 +1106,10 @@ int cmd_clone(int argc, const char **argv, const char *prefix)* apply the remote name provided by --origin only after this second * call to git_config, to ensure it overrides all config-based values. */ -if (option_origin !=NULL ) +if (option_origin !=NULL ) { +free (remote_name); remote_name =xstrdup (option_origin); + }if (remote_name ==NULL ) remote_name =xstrdup ("origin" );
Quoted 17 lines · Junio C Hamano
Perhaps a Coccinelle rule like this might have caught similar leaks:
@@
expression E;
expression V;
@@
- if (E)
- V = xstrdup(E);
+ if (E) {
+ free(V);
+ V = xstrdup(E);
+ }The fact that the result of
xstrdup()is assigned to V is that V is meant to hold a pointer to an allocated piece of memory.
Quoted 6 lines
With the preimage of the above semantic patch, it is reasonable to expect that V may be initialized to NULL or may be holding a pointer to a piece of allocated memory when the control reaches here, because otherwise, V will be either need to be freed (when E was not NULL, in which case we assigned the result of
xstrdup()to it) or V has garbage that cannot be freed later.
Initially, I did think "what if V is not initialized to NULL?" but you are right that the code would already be broken in that case.
builtin/clone.c int cmd_clone(int argc, const char **argv, const char *prefix) · line 1109
Quoted 1 line
builtin/clone.c +0
-1-if (option_origin !=NULL )
This technically wouldn't hit your rule, since "E" isn't just the variable name, as we typically do with our style. Is that something that Coccinelle automatically simplifies?
builtin/clone.c int cmd_clone(int argc, const char **argv, const char *prefix) · line 1109
Quoted 1 line
builtin/clone.c +1
-0+if (option_origin !=NULL ) {
Do you want to take this opportunity to drop the "!= NULL" here?
Quoted 4 lines
builtin/clone.c +2
-0+free (remote_name); remote_name =xstrdup (option_origin); + }Quoted 1 line
if (
remote_name== NULL)
Or do you want to keep similar style from the surrounding code?
Either way, looks good to me.
Thanks,
-Stolee
Quoted 10 lines · Derrick Stolee
builtin/clone.c int cmd_clone(int argc, const char **argv, const char *prefix) · line 1109
Quoted 1 line
builtin/clone.c +0
-1-if (option_origin !=NULL )This technically wouldn't hit your rule, since "E" isn't just the variable name, as we typically do with our style. Is that something that Coccinelle automatically simplifies?
builtin/clone.c int cmd_clone(int argc, const char **argv, const char *prefix) · line 1109
Quoted 1 line
builtin/clone.c +1
-0+if (option_origin !=NULL ) {Do you want to take this opportunity to drop the "!= NULL" here?
Quoted 6 lines
Quoted 4 lines
builtin/clone.c +2
-0+free (remote_name); remote_name =xstrdup (option_origin); + }Quoted 1 line
if (
remote_name== NULL)Or do you want to keep similar style from the surrounding code?
I think that it is better to leave that particular clean-up to the equals-null.cocci topic started by Elia; I know having them separate would cause a merge conflict, but even if I change them here, it will result in the same merge conflict anyway ;-)
CC'ing Elia as per the mention. Thread
https://lore.kernel.org/git/[email protected]/t/#u.
On 02/05/2022 18:12, Junio C Hamano wrote: <[email protected]>
Quoted 19 lines
Quoted 5 lines · Derrick Stolee
builtin/clone.c int cmd_clone(int argc, const char **argv, const char *prefix) · line 1109
Quoted 1 line
builtin/clone.c +0
-1-if (option_origin !=NULL )This technically wouldn't hit your rule, since "E" isn't just the variable name, as we typically do with our style. Is that something that Coccinelle automatically simplifies?
Quoted 8 lines
builtin/clone.c int cmd_clone(int argc, const char **argv, const char *prefix) · line 1109
Quoted 1 line
builtin/clone.c +1
-0+if (option_origin !=NULL ) {Do you want to take this opportunity to drop the "!= NULL" here?
Quoted 4 lines
builtin/clone.c +2
-0+free (remote_name); remote_name =xstrdup (option_origin); + }Quoted 1 line
if (
remote_name== NULL)Or do you want to keep similar style from the surrounding code?
I think that it is better to leave that particular clean-up to the
equals-null.coccitopic started by Elia; I know having them separate would cause a merge conflict, but even if I change them here, it will result in the same merge conflict anyway ;-)