On 5/18/22 5:22 AM, Eugene Syromiatnikov wrote:
Check that size would not overflow before calculation (and return
-EOVERFLOW if it will), to prevent potential out-of-bounds write
with the following copy_from_user. Add the same check
to kprobe_multi_resolve_syms in case it will be called from elsewhere
in the future.
Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
---
kernel/trace/bpf_trace.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d8553f4..212faa4 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2352,13 +2352,15 @@ static int
kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
unsigned long *addrs)
{
- unsigned long addr, size;
+ unsigned long addr, sym_size;
+ u32 size;
const char __user **syms;
int err = -ENOMEM;
unsigned int i;
char *func;
- size = cnt * sizeof(*syms);
+ if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
+ return -EOVERFLOW;
In mm/util.c kvmalloc_node(), we have
/* Don't even allow crazy sizes */
if (unlikely(size > INT_MAX)) {
WARN_ON_ONCE(!(flags & __GFP_NOWARN));
return NULL;
}
Basically the maximum size to be allocated in INT_MAX.
Here, we have 'size' as u32, which means if the size is 0xffff0000,
the check_mul_overflow will return false (no overflow) but
kvzalloc will still have a warning.
I think we should change the type of 'size' to be 'int' which
should catch the above case and be consistent with
what kvmalloc_node() intends to warn.
syms = kvzalloc(size, GFP_KERNEL);
if (!syms)
return -ENOMEM;
@@ -2382,9 +2384,9 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
addr = kallsyms_lookup_name(func);
if (!addr)
goto error;
- if (!kallsyms_lookup_size_offset(addr, &size, NULL))
+ if (!kallsyms_lookup_size_offset(addr, &sym_size, NULL))
goto error;
- addr = ftrace_location_range(addr, addr + size - 1);
+ addr = ftrace_location_range(addr, addr + sym_size - 1);
if (!addr)
goto error;
addrs[i] = addr;
@@ -2429,7 +2431,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
if (!cnt)
return -EINVAL;
- size = cnt * sizeof(*addrs);
+ if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
+ return -EOVERFLOW;
addrs = kvmalloc(size, GFP_KERNEL);
if (!addrs)
return -ENOMEM;
