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lib/test_scanf: Handle n_bits == 0 in random tests

PATCH In review Andy Shevchenko 3 participants 3 messages Jul 27, 2021 – Jul 30, 2021 Library code

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Andy Shevchenko

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#0 lore raw

PATCH 1/1 lib/test_scanf: Handle n_bits == 0 in random tests

UBSAN reported (via LKP)

[   11.021349][    T1] UBSAN: shift-out-of-bounds in lib/test_scanf.c:275:51
[   11.022782][    T1] shift exponent 32 is too large for 32-bit type 'unsigned int'

When n_bits == 0, the shift is out of range. Switch code to use GENMASK to handle this case.

Fixes 50f530e176ea ("lib: test_scanf: Add tests for sscanf number conversion")
Reported-by kernel test robot <[email protected]>
Signed-off-by Andy Shevchenko <[email protected]>
---
 lib/test_scanf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
lib/test_scanf.c +2 -2
index 84fe09eaf55e..abae88848972 100644
@@ -271,7 +271,7 @@ static u32 __init next_test_random(u32 max_bits)
 {
 	u32 n_bits = hweight32(prandom_u32_state(&rnd_state)) % (max_bits + 1);
 
-	return prandom_u32_state(&rnd_state) & (UINT_MAX >> (32 - n_bits));
+	return prandom_u32_state(&rnd_state) & GENMASK(n_bits, 0);
 }
 
 static unsigned long long __init next_test_random_ull(void)

@@ -280,7 +280,7 @@ static unsigned long long __init next_test_random_ull(void)
 	u32 n_bits = (hweight32(rand1) * 3) % 64;
 	u64 val = (u64)prandom_u32_state(&rnd_state) * rand1;
 
-	return val & (ULLONG_MAX >> (64 - n_bits));
+	return val & GENMASK_ULL(n_bits, 0);
 }
 
 #define random_for_type(T)				\
Signature · 1 line
2.30.2
Reviewed-by on v1 1/1
#1 lore raw
Quoted 5 lines · Andy Shevchenko

UBSAN reported (via LKP)

[   11.021349][    T1] UBSAN: shift-out-of-bounds in lib/test_scanf.c:275:51
[   11.022782][    T1] shift exponent 32 is too large for 32-bit type 'unsigned int'
Quoted 7 lines

When n_bits == 0, the shift is out of range. Switch code to use GENMASK to handle this case.

Fixes 50f530e176ea ("lib: test_scanf: Add tests for sscanf number conversion")
Reported-by kernel test robot <[email protected]>
Signed-off-by Andy Shevchenko <[email protected]>

---

Reviewed-by Richard Fitzgerald <[email protected]>

Sorry about that. Would have been sensible to use GENMASK anyway.

#2 lore raw
In reply to Andy Shevchenko
Quoted 11 lines · Andy Shevchenko

UBSAN reported (via LKP)

[   11.021349][    T1] UBSAN: shift-out-of-bounds in lib/test_scanf.c:275:51
[   11.022782][    T1] shift exponent 32 is too large for 32-bit type 'unsigned int'

When n_bits == 0, the shift is out of range. Switch code to use GENMASK to handle this case.

Fixes 50f530e176ea ("lib: test_scanf: Add tests for sscanf number conversion")
Reported-by kernel test robot <[email protected]>
Signed-off-by Andy Shevchenko <[email protected]>

The patch is committed in linux/printk.git, branch for-5.15.

I would send it for 4.14 if there was another urgent fix needed. But this one does not look important enough to hurry it up alone.

Best Regards,
Petr