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* [musl] [PATCH] fix undefined behavior from large shifts
@ 2022-06-04 17:25 NRK
  2022-06-04 18:04 ` Pascal Cuoq
  0 siblings, 1 reply; 4+ messages in thread
From: NRK @ 2022-06-04 17:25 UTC (permalink / raw)
  To: musl

int maybe 16bits in which case shifting left by 16 is UB.
cast to uint32_t before doing the shift to avoid such issues.
---
 src/string/memmem.c | 8 ++++----
 src/string/strstr.c | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/string/memmem.c b/src/string/memmem.c
index 11eff86e..4d19a922 100644
--- a/src/string/memmem.c
+++ b/src/string/memmem.c
@@ -12,8 +12,8 @@ static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned cha
 
 static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
-	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8;
-	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8;
+	uint32_t nw = (uint32_t)n[0]<<24 | (uint32_t)n[1]<<16 | n[2]<<8;
+	uint32_t hw = (uint32_t)h[0]<<24 | (uint32_t)h[1]<<16 | h[2]<<8;
 	for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
 		if (hw == nw) return (char *)h-3;
 	return hw == nw ? (char *)h-3 : 0;
@@ -21,8 +21,8 @@ static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned c
 
 static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
-	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
-	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+	uint32_t nw = (uint32_t)n[0]<<24 | (uint32_t)n[1]<<16 | n[2]<<8 | n[3];
+	uint32_t hw = (uint32_t)h[0]<<24 | (uint32_t)h[1]<<16 | h[2]<<8 | h[3];
 	for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
 		if (hw == nw) return (char *)h-4;
 	return hw == nw ? (char *)h-4 : 0;
diff --git a/src/string/strstr.c b/src/string/strstr.c
index 96657bc2..a68c1adb 100644
--- a/src/string/strstr.c
+++ b/src/string/strstr.c
@@ -10,16 +10,16 @@ static char *twobyte_strstr(const unsigned char *h, const unsigned char *n)
 
 static char *threebyte_strstr(const unsigned char *h, const unsigned char *n)
 {
-	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8;
-	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8;
+	uint32_t nw = (uint32_t)n[0]<<24 | (uint32_t)n[1]<<16 | n[2]<<8;
+	uint32_t hw = (uint32_t)h[0]<<24 | (uint32_t)h[1]<<16 | h[2]<<8;
 	for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8);
 	return *h ? (char *)h-2 : 0;
 }
 
 static char *fourbyte_strstr(const unsigned char *h, const unsigned char *n)
 {
-	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
-	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+	uint32_t nw = (uint32_t)n[0]<<24 | (uint32_t)n[1]<<16 | n[2]<<8 | n[3];
+	uint32_t hw = (uint32_t)h[0]<<24 | (uint32_t)h[1]<<16 | h[2]<<8 | h[3];
 	for (h+=3; *h && hw != nw; hw = hw<<8 | *++h);
 	return *h ? (char *)h-3 : 0;
 }
-- 
2.35.1


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2022-06-04 18:56 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-06-04 17:25 [musl] [PATCH] fix undefined behavior from large shifts NRK
2022-06-04 18:04 ` Pascal Cuoq
2022-06-04 18:16   ` Rich Felker
2022-06-04 18:55     ` NRK

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