Hi,
This is v2 of the fix & selftest previously sent at: https://lore.kernel.org/linux-mm/20221108195211.214025-1-flaniel@linux.micro...
Changes v1 to v2: - add 'cc:stable', 'Fixes:' and review/ack tags - update commitmsg and fix my email - rebase on bpf tree and tag for bpf tree
Thanks!
Alban Crequy (2): maccess: fix writing offset in case of fault in strncpy_from_kernel_nofault() selftests: bpf: add a test when bpf_probe_read_kernel_str() returns EFAULT
mm/maccess.c | 2 +- tools/testing/selftests/bpf/prog_tests/varlen.c | 7 +++++++ tools/testing/selftests/bpf/progs/test_varlen.c | 5 +++++ 3 files changed, 13 insertions(+), 1 deletion(-)
If a page fault occurs while copying the first byte, this function resets one byte before dst. As a consequence, an address could be modified and leaded to kernel crashes if case the modified address was accessed later.
Fixes: b58294ead14c ("maccess: allow architectures to provide kernel probing directly") Cc: stable@vger.kernel.org [5.8] Signed-off-by: Alban Crequy albancrequy@linux.microsoft.com Tested-by: Francis Laniel flaniel@linux.microsoft.com Reviewed-by: Andrew Morton akpm@linux-foundation.org
---
Changes v1 to v2: - add 'cc:stable', 'Fixes:' and review tag - fix my email - rebase on bpf tree and tag for bpf tree --- mm/maccess.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/maccess.c b/mm/maccess.c index 5f4d240f67ec..074f6b086671 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -97,7 +97,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count) return src - unsafe_addr; Efault: pagefault_enable(); - dst[-1] = '\0'; + dst[0] = '\0'; return -EFAULT; }
This commit tests previous fix of bpf_probe_read_kernel_str().
The BPF helper bpf_probe_read_kernel_str should return -EFAULT when given a bad source pointer and the target buffer should only be modified to make the string NULL terminated.
bpf_probe_read_kernel_str() was previously inserting a NULL before the beginning of the dst buffer. This test should ensure that the implementation stays correct for now on.
Without the fix, this test will fail as follows: $ cd tools/testing/selftests/bpf $ make $ sudo ./test_progs --name=varlen ... test_varlen:FAIL:check got 0 != exp 66
Signed-off-by: Alban Crequy albancrequy@linux.microsoft.com Signed-off-by: Francis Laniel flaniel@linux.microsoft.com Acked-by: Yonghong Song yhs@fb.com
Changes v1 to v2: - add ack tag - fix my email - rebase on bpf tree and tag for bpf tree --- tools/testing/selftests/bpf/prog_tests/varlen.c | 7 +++++++ tools/testing/selftests/bpf/progs/test_varlen.c | 5 +++++ 2 files changed, 12 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/varlen.c b/tools/testing/selftests/bpf/prog_tests/varlen.c index dd324b4933db..4d7056f8f177 100644 --- a/tools/testing/selftests/bpf/prog_tests/varlen.c +++ b/tools/testing/selftests/bpf/prog_tests/varlen.c @@ -63,6 +63,13 @@ void test_varlen(void) CHECK_VAL(data->total4, size1 + size2); CHECK(memcmp(data->payload4, exp_str, size1 + size2), "content_check", "doesn't match!\n"); + + CHECK_VAL(bss->ret_bad_read, -EFAULT); + CHECK_VAL(data->payload_bad[0], 0x42); + CHECK_VAL(data->payload_bad[1], 0x42); + CHECK_VAL(data->payload_bad[2], 0); + CHECK_VAL(data->payload_bad[3], 0x42); + CHECK_VAL(data->payload_bad[4], 0x42); cleanup: test_varlen__destroy(skel); } diff --git a/tools/testing/selftests/bpf/progs/test_varlen.c b/tools/testing/selftests/bpf/progs/test_varlen.c index 3987ff174f1f..20eb7d422c41 100644 --- a/tools/testing/selftests/bpf/progs/test_varlen.c +++ b/tools/testing/selftests/bpf/progs/test_varlen.c @@ -19,6 +19,7 @@ __u64 payload1_len1 = 0; __u64 payload1_len2 = 0; __u64 total1 = 0; char payload1[MAX_LEN + MAX_LEN] = {}; +__u64 ret_bad_read = 0;
/* .data */ int payload2_len1 = -1; @@ -36,6 +37,8 @@ int payload4_len2 = -1; int total4= -1; char payload4[MAX_LEN + MAX_LEN] = { 1 };
+char payload_bad[5] = { 0x42, 0x42, 0x42, 0x42, 0x42 }; + SEC("raw_tp/sys_enter") int handler64_unsigned(void *regs) { @@ -61,6 +64,8 @@ int handler64_unsigned(void *regs)
total1 = payload - (void *)payload1;
+ ret_bad_read = bpf_probe_read_kernel_str(payload_bad + 2, 1, (void *) -1); + return 0; }
Hello:
This series was applied to bpf/bpf.git (master) by Andrii Nakryiko andrii@kernel.org:
On Thu, 10 Nov 2022 09:56:12 +0100 you wrote:
Hi,
This is v2 of the fix & selftest previously sent at: https://lore.kernel.org/linux-mm/20221108195211.214025-1-flaniel@linux.micro...
Changes v1 to v2:
- add 'cc:stable', 'Fixes:' and review/ack tags
- update commitmsg and fix my email
- rebase on bpf tree and tag for bpf tree
[...]
Here is the summary with links: - [bpf,v2,1/2] maccess: fix writing offset in case of fault in strncpy_from_kernel_nofault() https://git.kernel.org/bpf/bpf/c/8678ea06852c - [bpf,v2,2/2] selftests: bpf: add a test when bpf_probe_read_kernel_str() returns EFAULT https://git.kernel.org/bpf/bpf/c/9cd094829dae
You are awesome, thank you!
linux-kselftest-mirror@lists.linaro.org
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Alban Crequy -
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