On Fri, 29 Jun 2018 21:44:53 +0300 Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote: > Signed integer overflow is undefined according to the C standard. > The overflow in ksys_fadvise64_64() is deliberate, but since it is signed > overflow, UBSAN complains: > UBSAN: Undefined behaviour in mm/fadvise.c:76:10 > signed integer overflow: > 4 + 9223372036854775805 cannot be represented in type 'long long int' > > Use unsigned types to do math. Unsigned overflow is defined so UBSAN > will not complain about it. This patch doesn't change generated code. > > ... > > --- a/mm/fadvise.c > +++ b/mm/fadvise.c > @@ -73,7 +73,7 @@ int ksys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice) > } > > /* Careful about overflows. Len == 0 means "as much as possible" */ > - endbyte = offset + len; > + endbyte = (u64)offset + (u64)len; > if (!len || endbyte < len) > endbyte = -1; > else Readers of this code will wonder "what the heck are those casts for". Therefore: --- a/mm/fadvise.c~mm-fadvise-fix-signed-overflow-ubsan-complaint-fix +++ a/mm/fadvise.c @@ -72,7 +72,11 @@ int ksys_fadvise64_64(int fd, loff_t off goto out; } - /* Careful about overflows. Len == 0 means "as much as possible" */ + /* + * Careful about overflows. Len == 0 means "as much as possible". Use + * unsigned math because signed overflows are undefined and UBSan + * complains. + */ endbyte = (u64)offset + (u64)len; if (!len || endbyte < len) endbyte = -1; _
