Commit 65ab5ac4 authored by Jordan Rome's avatar Jordan Rome Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_copy_from_user_str kfunc 



This adds a kfunc wrapper around strncpy_from_user,
which can be called from sleepable BPF programs.

This matches the non-sleepable 'bpf_probe_read_user_str'
helper except it includes an additional 'flags'
param, which allows consumers to clear the entire
destination buffer on success or failure.

Signed-off-by: default avatarJordan Rome <linux@jordanrome.com>
Link: https://lore.kernel.org/r/20240823195101.3621028-1-linux@jordanrome.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 5772c345

include/uapi/linux/bpf.h

+9 −0
Original line number Diff line number Diff line
@@ -7513,4 +7513,13 @@ struct bpf_iter_num { 
	__u64 __opaque[1];

} __attribute__((aligned(8)));



/*

 * Flags to control BPF kfunc behaviour.

 *     - BPF_F_PAD_ZEROS: Pad destination buffer with zeros. (See the respective

 *       helper documentation for details.)

 */

enum bpf_kfunc_flags {

	BPF_F_PAD_ZEROS = (1ULL << 0),

};



#endif /* _UAPI__LINUX_BPF_H__ */

kernel/bpf/helpers.c

+42 −0
Original line number Diff line number Diff line
@@ -2962,6 +2962,47 @@ __bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it) 
	bpf_mem_free(&bpf_global_ma, kit->bits);

}



/**

 * bpf_copy_from_user_str() - Copy a string from an unsafe user address

 * @dst:             Destination address, in kernel space.  This buffer must be

 *                   at least @dst__sz bytes long.

 * @dst__sz:         Maximum number of bytes to copy, includes the trailing NUL.

 * @unsafe_ptr__ign: Source address, in user space.

 * @flags:           The only supported flag is BPF_F_PAD_ZEROS

 *

 * Copies a NUL-terminated string from userspace to BPF space. If user string is

 * too long this will still ensure zero termination in the dst buffer unless

 * buffer size is 0.

 *

 * If BPF_F_PAD_ZEROS flag is set, memset the tail of @dst to 0 on success and

 * memset all of @dst on failure.

 */

__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__sz, const void __user *unsafe_ptr__ign, u64 flags)

{

	int ret;



	if (unlikely(flags & ~BPF_F_PAD_ZEROS))

		return -EINVAL;



	if (unlikely(!dst__sz))

		return 0;



	ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__sz - 1);

	if (ret < 0) {

		if (flags & BPF_F_PAD_ZEROS)

			memset((char *)dst, 0, dst__sz);



		return ret;

	}



	if (flags & BPF_F_PAD_ZEROS)

		memset((char *)dst + ret, 0, dst__sz - ret);

	else

		((char *)dst)[ret] = '\0';



	return ret + 1;

}



__bpf_kfunc_end_defs();



BTF_KFUNCS_START(generic_btf_ids)
@@ -3047,6 +3088,7 @@ BTF_ID_FLAGS(func, bpf_preempt_enable) 
BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)

BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)

BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)

BTF_KFUNCS_END(common_btf_ids)



static const struct btf_kfunc_id_set common_kfunc_set = {

tools/include/uapi/linux/bpf.h

+9 −0
Original line number Diff line number Diff line
@@ -7512,4 +7512,13 @@ struct bpf_iter_num { 
	__u64 __opaque[1];

} __attribute__((aligned(8)));



/*

 * Flags to control BPF kfunc behaviour.

 *     - BPF_F_PAD_ZEROS: Pad destination buffer with zeros. (See the respective

 *       helper documentation for details.)

 */

enum bpf_kfunc_flags {

	BPF_F_PAD_ZEROS = (1ULL << 0),

};



#endif /* _UAPI__LINUX_BPF_H__ */