mtd: phram: Prevent divide by zero bug in phram_setup()
Subsystems (3)
PATCH 1/1 mtd: phram: Prevent divide by zero bug in phram_setup()
The problem is that "erasesize" is a uint32_t type so it might be non-zero but the truncated "(uint32_t)erasesize" value *is* zero. That would lead to the divide by zero bug.
Avoid the bug by delaying the divide until after we have validated that "erasesize" is reasonable.
--- drivers/mtd/devices/phram.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
drivers/mtd/devices/phram.c +8 -4
@@ -264,16 +264,20 @@ static int phram_setup(const char *val) } } -if (erasesize) -div_u64_rem (len, (uint32_t )erasesize, &rem); -if (len ==0 || erasesize ==0 || erasesize > len - || erasesize >UINT_MAX || rem) { + || erasesize >UINT_MAX ) {parse_err ("illegal erasesize or len\n" ); ret = -EINVAL ; goto error; } +div_u64_rem (len, (uint32_t )erasesize, &rem); +if (rem) { +parse_err ("len is not multiple of erasesize\n" ); + ret = -EINVAL ; + goto error; + } + ret =register_device (name, start, len, (uint32_t )erasesize);if (ret) goto error;
Signature · 1 line
2.20.1
Miquel Raynal
maintainerHi Dan,
[email protected] wrote on Fri, 21 Jan 2022 08:38:36 +0300:
Quoted 1 line
The problem is that "erasesize" is a
uint32_ttype so it might be
Don't you mean uint64_t here? Otherwise I don't get the sentence.
Quoted 1 line
non-zero but the truncated "(uint32_t)erasesize" value *is* zero. That
s/*is*/*can* be/ ? (again, if my understanding is correct).
Quoted 4 lines
would lead to the divide by zero bug.
Avoid the bug by delaying the divide until after we have validated that "erasesize" is reasonable.
I don't really get the fix. If "erasesize" is big enough, then (uint32_t)erasesize can however be zero. But checking if erasesize is zero beforehands does not fix the situation. Or am I missing something?
Quoted 25 lines
Fixes dc2b3e5cbc80 ("mtd: phram: use div_u64_rem to stop overwrite len in phram_setup")Signed-off-by Dan Carpenter <[email protected]>--- drivers/mtd/devices/phram.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)drivers/mtd/devices/phram.c +1
-4@@ -264,16 +264,20 @@ static int phram_setup(const char *val) } } -if (erasesize) -div_u64_rem (len, (uint32_t )erasesize, &rem); -if (len ==0 || erasesize ==0 || erasesize > len - || erasesize >UINT_MAX || rem) { + || erasesize >UINT_MAX ) {parse_err ("illegal erasesize or len\n" ); ret = -EINVAL ; goto error; }
drivers/mtd/devices/phram.c static int phram_setup(const char *val) · line 283
Quoted 10 lines
drivers/mtd/devices/phram.c +7
-0+div_u64_rem (len, (uint32_t )erasesize, &rem); +if (rem) { +parse_err ("len is not multiple of erasesize\n" ); + ret = -EINVAL ; + goto error; + } + ret =register_device (name, start, len, (uint32_t )erasesize);if (ret) goto error;
Thanks,
Miquèl
Quoted 8 lines · Miquel Raynal
Hi Dan,
[email protected] wrote on Fri, 21 Jan 2022 08:38:36 +0300:
Quoted 1 line
The problem is that "erasesize" is a
uint32_ttype so it might beDon't you mean
uint64_there? Otherwise I don't get the sentence.
Yeah. I meant uint64_t. Will resend.
Quoted 4 lines
Quoted 1 line
non-zero but the truncated "(uint32_t)erasesize" value *is* zero. That
s/*is*/*can* be/ ? (again, if my understanding is correct).
It might be a situation where "erasesize" is non-zero but after we truncated it "(uint32_t)erasesize" is zero.
Quoted 9 lines
Quoted 4 lines
would lead to the divide by zero bug.
Avoid the bug by delaying the divide until after we have validated that "erasesize" is reasonable.
I don't really get the fix. If "erasesize" is big enough, then (uint32_t)erasesize can however be zero. But checking if erasesize is zero beforehands does not fix the situation. Or am I missing something?
It doesn't just check for zero, it checks a couple other things including if erasesize > UINT_MAX.
regards,
dan carpenter
Thanks for the fix!
Quoted 43 lines · Dan Carpenter
The problem is that "erasesize" is a
uint32_ttype so it might be non-zero but the truncated "(uint32_t)erasesize" value *is* zero. That would lead to the divide by zero bug.Avoid the bug by delaying the divide until after we have validated that "erasesize" is reasonable.
Fixes dc2b3e5cbc80 ("mtd: phram: use div_u64_rem to stop overwrite len in phram_setup")Signed-off-by Dan Carpenter <[email protected]>--- drivers/mtd/devices/phram.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)drivers/mtd/devices/phram.c +8
-4@@ -264,16 +264,20 @@ static int phram_setup(const char *val) } } -if (erasesize) -div_u64_rem (len, (uint32_t )erasesize, &rem); -if (len ==0 || erasesize ==0 || erasesize > len - || erasesize >UINT_MAX || rem) { + || erasesize >UINT_MAX ) {parse_err ("illegal erasesize or len\n" ); ret = -EINVAL ; goto error; } +div_u64_rem (len, (uint32_t )erasesize, &rem); +if (rem) { +parse_err ("len is not multiple of erasesize\n" ); + ret = -EINVAL ; + goto error; + } + ret =register_device (name, start, len, (uint32_t )erasesize);if (ret) goto error;