nfs: fix undefined behavior in nfs_block_bits()

Sergey Shtylyov · Trond Myklebust · commit 3c0a2e0b0ae6 · 2024-05-21T08:34:15.000-04:00
Shifting *signed int* typed constant 1 left by 31 bits causes undefined
behavior. Specify the correct *unsigned long* type by using 1UL instead.

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Cc: stable@vger.kernel.org
Signed-off-by: Sergey Shtylyov &lt;s.shtylyov@omp.ru&gt;
Reviewed-by: Benjamin Coddington &lt;bcodding@redhat.com&gt;
Signed-off-by: Trond Myklebust &lt;trond.myklebust@hammerspace.com&gt;
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
@@ -717,9 +717,9 @@ unsigned long nfs_block_bits(unsigned long bsize, unsigned char *nrbitsp)
 	if ((bsize & (bsize - 1)) || nrbitsp) {
 		unsigned char	nrbits;
 
-		for (nrbits = 31; nrbits && !(bsize & (1 << nrbits)); nrbits--)
+		for (nrbits = 31; nrbits && !(bsize & (1UL << nrbits)); nrbits--)
 			;
-		bsize = 1 << nrbits;
+		bsize = 1UL << nrbits;
 		if (nrbitsp)
 			*nrbitsp = nrbits;
 	}

Original file line number	Diff line number	Diff line change
`@@ -717,9 +717,9 @@ unsigned long nfs_block_bits(unsigned long bsize, unsigned char *nrbitsp)`
`717`	`717`	`if ((bsize & (bsize - 1)) \|\| nrbitsp) {`
`718`	`718`	`unsigned char nrbits;`
`719`	`719`
`720`		`- for (nrbits = 31; nrbits && !(bsize & (1 << nrbits)); nrbits--)`
	`720`	`+ for (nrbits = 31; nrbits && !(bsize & (1UL << nrbits)); nrbits--)`
`721`	`721`	`;`
`722`		`- bsize = 1 << nrbits;`
	`722`	`+ bsize = 1UL << nrbits;`
`723`	`723`	`if (nrbitsp)`
`724`	`724`	`*nrbitsp = nrbits;`
`725`	`725`	`}`