[PATCH 2.6.15-rc7] udf/balloc.c : Fix use of uninitialized data

[PATCH 2.6.15-rc7] udf/balloc.c : Fix use of uninitialized data

[Parag Warudkar]

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2.6.15-rc7 - GCC warns correctly -
 fs/udf/balloc.c: In function 'udf_table_new_block':
 fs/udf/balloc.c:757: warning: 'goal_eloc.logicalBlockNum' may be used
uninitialized in this function

Variable goal_eloc is automatic, non-static and initialized conditionally -

 if (nspread < spread)
 {
     ...........
     goal_eloc = eloc;
     ...........
 }

 The following patch fixes this by initializing the goal_eloc variable to zero.
Hopefully zero should be better than some random data! (Patch also
attached in case of problem with below inline version.) Compile
tested.

--- linux-2.6/fs/udf/balloc.c.orig      2005-12-28 11:53:12.000000000 -0500
+++ linux-2.6/fs/udf/balloc.c   2005-12-28 11:53:19.000000000 -0500
@@ -754,7 +754,8 @@ static int udf_table_new_block(struct su
        uint32_t spread = 0xFFFFFFFF, nspread = 0xFFFFFFFF;
        uint32_t newblock = 0, adsize;
        uint32_t extoffset, goal_extoffset, elen, goal_elen = 0;
-       kernel_lb_addr bloc, goal_bloc, eloc, goal_eloc;
+       kernel_lb_addr bloc, goal_bloc, eloc,
+       goal_eloc = { .logicalBlockNum=0, .partitionReferenceNum=0 } ;
        struct buffer_head *bh, *goal_bh;
        int8_t etype;

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--- linux-2.6/fs/udf/balloc.c.orig	2005-12-28 11:53:12.000000000 -0500
+++ linux-2.6/fs/udf/balloc.c	2005-12-28 11:53:19.000000000 -0500
@@ -754,7 +754,8 @@ static int udf_table_new_block(struct su
 	uint32_t spread = 0xFFFFFFFF, nspread = 0xFFFFFFFF;
 	uint32_t newblock = 0, adsize;
 	uint32_t extoffset, goal_extoffset, elen, goal_elen = 0;
-	kernel_lb_addr bloc, goal_bloc, eloc, goal_eloc;
+	kernel_lb_addr bloc, goal_bloc, eloc, 
+	goal_eloc = { .logicalBlockNum=0, .partitionReferenceNum=0 } ;
 	struct buffer_head *bh, *goal_bh;
 	int8_t etype;
 

Re: [PATCH 2.6.15-rc7] udf/balloc.c : Fix use of uninitialized data

[Parag Warudkar]

Forgot to add Signed-off-by - corrected patch follows -

Signed-off-by: Parag Warudkar <parag.warudkar@gmail.com>

Variable goal_eloc is automatic, non-static and initialized conditionally.
 The following patch fixes this by initializing the goal_eloc variable to zero.
Hopefully zero should be better than some random data! (Patch also
attached in case of problem with below inline version.) Compile
tested.

--- linux-2.6/fs/udf/balloc.c.orig      2005-12-28 11:53:12.000000000 -0500
+++ linux-2.6/fs/udf/balloc.c   2005-12-28 11:53:19.000000000 -0500
@@ -754,7 +754,8 @@ static int udf_table_new_block(struct su
        uint32_t spread = 0xFFFFFFFF, nspread = 0xFFFFFFFF;
        uint32_t newblock = 0, adsize;
        uint32_t extoffset, goal_extoffset, elen, goal_elen = 0;
-       kernel_lb_addr bloc, goal_bloc, eloc, goal_eloc;
+       kernel_lb_addr bloc, goal_bloc, eloc,
+       goal_eloc = { .logicalBlockNum=0, .partitionReferenceNum=0 } ;
        struct buffer_head *bh, *goal_bh;
        int8_t etype;

Re: [PATCH 2.6.15-rc7] udf/balloc.c : Fix use of uninitialized data

[Al Viro]

On Wed, Dec 28, 2005 at 12:13:37PM -0500, Parag Warudkar wrote:
> 2.6.15-rc7 - GCC warns correctly -
>  fs/udf/balloc.c: In function 'udf_table_new_block':
>  fs/udf/balloc.c:757: warning: 'goal_eloc.logicalBlockNum' may be used
> uninitialized in this function
> 
> Variable goal_eloc is automatic, non-static and initialized conditionally -
> 
>  if (nspread < spread)
>  {
>      ...........
>      goal_eloc = eloc;
>      ...........
>  }
> 
>  The following patch fixes this by initializing the goal_eloc variable to zero.
> Hopefully zero should be better than some random data!

Wrong.  RTFS, please.  They have

	spread = 0xffffffff;
	while (....) {
		...
		if (nspread < spread) {
			spread = nspread;
			...
			goal_eloc = eloc;
			...
		}
		...
	}
	...
	if (spread == 0xffffffff) {
		...
		return 0;
	}
	....
	use goal_eloc

which is absolutely correct - to reach the use of goal_eloc we have to
have passed through reassignment of spread between spread = 0xffffffff
and departure via if (spread == 0xffffffff).  Such reassignment could
happen only in one block and in the same block we have assignment to
goal_eloc.