| Message ID | 20230120135651.24816-1-rpalethorpe@suse.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | tst_assert: Fix buffer overflow in scanf | expand |
Hi! > The maximum field width of a string conversion does not include the > null byte. So we can overflow the buffer by one byte. > > This can be triggered in ioctl_loop01 with -fsanitize=address even if > the file contents are far less than the buffer size: > > tst_test.c:1558: TINFO: Timeout per run is 0h 00m 30s > tst_device.c:93: TINFO: Found free device 1 '/dev/loop1' > ioctl_loop01.c:85: TPASS: /sys/block/loop1/loop/partscan = 0 > ioctl_loop01.c:86: TPASS: /sys/block/loop1/loop/autoclear = 0 > ================================================================= > ==293==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xf5c03420 at pc 0xf7952bf8 bp 0xff9cf9f8 sp 0xff9cf5d0 > WRITE of size 1025 at 0xf5c03420 thread T0 > #0 0xf7952bf7 (/lib/libasan.so.8+0x89bf7) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) > #1 0xf7953879 in __isoc99_vfscanf (/lib/libasan.so.8+0x8a879) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) > #2 0x8071f85 in safe_file_scanf /home/rich/qa/ltp/lib/safe_file_ops.c:139 > #3 0x80552ea in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:60 > #4 0x804f17a in verify_ioctl_loop /home/rich/qa/ltp/testcases/kernel/syscalls/ioctl/ioctl_loop01.c:87 > #5 0x8061599 in run_tests /home/rich/qa/ltp/lib/tst_test.c:1380 > #6 0x8061599 in testrun /home/rich/qa/ltp/lib/tst_test.c:1463 > #7 0x8061599 in fork_testrun /home/rich/qa/ltp/lib/tst_test.c:1592 > #8 0x806877a in tst_run_tcases /home/rich/qa/ltp/lib/tst_test.c:1686 > #9 0x804e01b in main ../../../../include/tst_test.h:394 > #10 0xf7188294 in __libc_start_call_main (/lib/libc.so.6+0x23294) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) > #11 0xf7188357 in __libc_start_main@@GLIBC_2.34 (/lib/libc.so.6+0x23357) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) > #12 0x804e617 in _start ../sysdeps/i386/start.S:111 > > Address 0xf5c03420 is located in stack of thread T0 at offset 1056 in frame > #0 0x805525f in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:57 > > This frame has 1 object(s): > [32, 1056) 'sys_val' (line 58) <== Memory access at offset 1056 overflows this variable Uff, looking closely at the scanf manual: String input conversions store a terminating null byte ('\0') to mark the end of the input; the maximum field width does not include this terminator. So do I get it right that scanf() actually writes one byte after the size passed after the % character? That sounds a bit evil to me. Anyways: Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
Hello, Cyril Hrubis <chrubis@suse.cz> writes: > Hi! >> The maximum field width of a string conversion does not include the >> null byte. So we can overflow the buffer by one byte. >> >> This can be triggered in ioctl_loop01 with -fsanitize=address even if >> the file contents are far less than the buffer size: >> >> tst_test.c:1558: TINFO: Timeout per run is 0h 00m 30s >> tst_device.c:93: TINFO: Found free device 1 '/dev/loop1' >> ioctl_loop01.c:85: TPASS: /sys/block/loop1/loop/partscan = 0 >> ioctl_loop01.c:86: TPASS: /sys/block/loop1/loop/autoclear = 0 >> ================================================================= >> ==293==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xf5c03420 at pc 0xf7952bf8 bp 0xff9cf9f8 sp 0xff9cf5d0 >> WRITE of size 1025 at 0xf5c03420 thread T0 >> #0 0xf7952bf7 (/lib/libasan.so.8+0x89bf7) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) >> #1 0xf7953879 in __isoc99_vfscanf (/lib/libasan.so.8+0x8a879) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) >> #2 0x8071f85 in safe_file_scanf /home/rich/qa/ltp/lib/safe_file_ops.c:139 >> #3 0x80552ea in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:60 >> #4 0x804f17a in verify_ioctl_loop /home/rich/qa/ltp/testcases/kernel/syscalls/ioctl/ioctl_loop01.c:87 >> #5 0x8061599 in run_tests /home/rich/qa/ltp/lib/tst_test.c:1380 >> #6 0x8061599 in testrun /home/rich/qa/ltp/lib/tst_test.c:1463 >> #7 0x8061599 in fork_testrun /home/rich/qa/ltp/lib/tst_test.c:1592 >> #8 0x806877a in tst_run_tcases /home/rich/qa/ltp/lib/tst_test.c:1686 >> #9 0x804e01b in main ../../../../include/tst_test.h:394 >> #10 0xf7188294 in __libc_start_call_main (/lib/libc.so.6+0x23294) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) >> #11 0xf7188357 in __libc_start_main@@GLIBC_2.34 (/lib/libc.so.6+0x23357) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) >> #12 0x804e617 in _start ../sysdeps/i386/start.S:111 >> >> Address 0xf5c03420 is located in stack of thread T0 at offset 1056 in frame >> #0 0x805525f in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:57 >> >> This frame has 1 object(s): >> [32, 1056) 'sys_val' (line 58) <== Memory access at offset 1056 overflows this variable > > Uff, looking closely at the scanf manual: > > String input conversions store a terminating null byte ('\0') to mark > the end of the input; the maximum field width does not include this > terminator. > > So do I get it right that scanf() actually writes one byte after the > size passed after the % character? That sounds a bit evil to me. Yes, I suppose the root cause is null terminated strings. ;-) > > Anyways: > > Reviewed-by: Cyril Hrubis <chrubis@suse.cz> Thanks
> Hello, > Cyril Hrubis <chrubis@suse.cz> writes: > > Hi! > >> The maximum field width of a string conversion does not include the > >> null byte. So we can overflow the buffer by one byte. > >> This can be triggered in ioctl_loop01 with -fsanitize=address even if > >> the file contents are far less than the buffer size: > >> tst_test.c:1558: TINFO: Timeout per run is 0h 00m 30s > >> tst_device.c:93: TINFO: Found free device 1 '/dev/loop1' > >> ioctl_loop01.c:85: TPASS: /sys/block/loop1/loop/partscan = 0 > >> ioctl_loop01.c:86: TPASS: /sys/block/loop1/loop/autoclear = 0 > >> ================================================================= > >> ==293==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xf5c03420 at pc 0xf7952bf8 bp 0xff9cf9f8 sp 0xff9cf5d0 > >> WRITE of size 1025 at 0xf5c03420 thread T0 > >> #0 0xf7952bf7 (/lib/libasan.so.8+0x89bf7) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) > >> #1 0xf7953879 in __isoc99_vfscanf (/lib/libasan.so.8+0x8a879) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) > >> #2 0x8071f85 in safe_file_scanf /home/rich/qa/ltp/lib/safe_file_ops.c:139 > >> #3 0x80552ea in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:60 > >> #4 0x804f17a in verify_ioctl_loop /home/rich/qa/ltp/testcases/kernel/syscalls/ioctl/ioctl_loop01.c:87 > >> #5 0x8061599 in run_tests /home/rich/qa/ltp/lib/tst_test.c:1380 > >> #6 0x8061599 in testrun /home/rich/qa/ltp/lib/tst_test.c:1463 > >> #7 0x8061599 in fork_testrun /home/rich/qa/ltp/lib/tst_test.c:1592 > >> #8 0x806877a in tst_run_tcases /home/rich/qa/ltp/lib/tst_test.c:1686 > >> #9 0x804e01b in main ../../../../include/tst_test.h:394 > >> #10 0xf7188294 in __libc_start_call_main (/lib/libc.so.6+0x23294) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) > >> #11 0xf7188357 in __libc_start_main@@GLIBC_2.34 (/lib/libc.so.6+0x23357) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) > >> #12 0x804e617 in _start ../sysdeps/i386/start.S:111 > >> Address 0xf5c03420 is located in stack of thread T0 at offset 1056 in frame > >> #0 0x805525f in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:57 > >> This frame has 1 object(s): > >> [32, 1056) 'sys_val' (line 58) <== Memory access at offset 1056 overflows this variable > > Uff, looking closely at the scanf manual: > > String input conversions store a terminating null byte ('\0') to mark > > the end of the input; the maximum field width does not include this > > terminator. > > So do I get it right that scanf() actually writes one byte after the > > size passed after the % character? That sounds a bit evil to me. > Yes, I suppose the root cause is null terminated strings. ;-) Interesting. I dared to merge it (added your Signed-off-by:). Thanks! Kind regards, Petr > > Anyways: > > Reviewed-by: Cyril Hrubis <chrubis@suse.cz> > Thanks
diff --git a/lib/tst_assert.c b/lib/tst_assert.c index 9b8ebc167..b68bd5d39 100644 --- a/lib/tst_assert.c +++ b/lib/tst_assert.c @@ -57,7 +57,7 @@ void tst_assert_str(const char *file, const int lineno, const char *path, const { char sys_val[1024]; - safe_file_scanf(file, lineno, NULL, path, "%1024s", sys_val); + safe_file_scanf(file, lineno, NULL, path, "%1023s", sys_val); if (!strcmp(val, sys_val)) { tst_res_(file, lineno, TPASS, "%s = '%s'", path, val); return; @@ -71,7 +71,7 @@ void tst_assert_file_str(const char *file, const int lineno, const char *path, c char sys_val[1024]; char fmt[2048]; - snprintf(fmt, sizeof(fmt), "%s: %%1024s", prefix); + snprintf(fmt, sizeof(fmt), "%s: %%1023s", prefix); file_lines_scanf(file, lineno, NULL, 1, path, fmt, sys_val); if (!strcmp(val, sys_val)) {
The maximum field width of a string conversion does not include the null byte. So we can overflow the buffer by one byte. This can be triggered in ioctl_loop01 with -fsanitize=address even if the file contents are far less than the buffer size: tst_test.c:1558: TINFO: Timeout per run is 0h 00m 30s tst_device.c:93: TINFO: Found free device 1 '/dev/loop1' ioctl_loop01.c:85: TPASS: /sys/block/loop1/loop/partscan = 0 ioctl_loop01.c:86: TPASS: /sys/block/loop1/loop/autoclear = 0 ================================================================= ==293==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xf5c03420 at pc 0xf7952bf8 bp 0xff9cf9f8 sp 0xff9cf5d0 WRITE of size 1025 at 0xf5c03420 thread T0 #0 0xf7952bf7 (/lib/libasan.so.8+0x89bf7) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) #1 0xf7953879 in __isoc99_vfscanf (/lib/libasan.so.8+0x8a879) (BuildId: f8d5331e88e5c1b8a8a55eda0a8e20503ea0d2b9) #2 0x8071f85 in safe_file_scanf /home/rich/qa/ltp/lib/safe_file_ops.c:139 #3 0x80552ea in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:60 #4 0x804f17a in verify_ioctl_loop /home/rich/qa/ltp/testcases/kernel/syscalls/ioctl/ioctl_loop01.c:87 #5 0x8061599 in run_tests /home/rich/qa/ltp/lib/tst_test.c:1380 #6 0x8061599 in testrun /home/rich/qa/ltp/lib/tst_test.c:1463 #7 0x8061599 in fork_testrun /home/rich/qa/ltp/lib/tst_test.c:1592 #8 0x806877a in tst_run_tcases /home/rich/qa/ltp/lib/tst_test.c:1686 #9 0x804e01b in main ../../../../include/tst_test.h:394 #10 0xf7188294 in __libc_start_call_main (/lib/libc.so.6+0x23294) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) #11 0xf7188357 in __libc_start_main@@GLIBC_2.34 (/lib/libc.so.6+0x23357) (BuildId: 87c7a50c8792985dd164f5af2d45b8e91d9f4391) #12 0x804e617 in _start ../sysdeps/i386/start.S:111 Address 0xf5c03420 is located in stack of thread T0 at offset 1056 in frame #0 0x805525f in tst_assert_str /home/rich/qa/ltp/lib/tst_assert.c:57 This frame has 1 object(s): [32, 1056) 'sys_val' (line 58) <== Memory access at offset 1056 overflows this variable Fixes: f4919b145a9e lib: Add TST_ASSERT_FILE_INT and TST_ASSERT_FILE_STR --- lib/tst_assert.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)