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dtrace: Fix /"string" == NULL/ comparisons using an uninitialized value.

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A test of this is funcs/tst.strtok.d which has this filter:

    BEGIN
    /(this->field = strtok(this->str, ",")) == NULL/
    {
            exit(1);
    }
The test will randomly fail with exit status of 1 indicating that this->field
was NULL even though printing it out shows it is not.

This is compiled to the DTrace instruction set:
    // Pushed arguments not shown here
    // call strtok() and set result into %r1
    07: 2f001f01    call DIF_SUBR(31), %r1          ! strtok
    // set thread local scalar this->field from %r1
    08: 39050101    stls %r1, DT_VAR(1281)          ! DT_VAR(1281) = "field"
    // Prepare for the == comparison
    // Set right side of %r2 to NULL
    09: 25000102    setx DT_INTEGER[1], %r2         ! 0x0
    // string compare %r1 (strtok result) to %r2
    10: 27010200    scmp %r1, %r2

In this case only %r1 is loaded with a string limit set to lim1.  %r2 being
NULL does not get loaded and does not set lim2.  Then we call dtrace_strncmp()
with MIN(lim1, lim2) resulting in passing 0 and comparing neither side.
dtrace_strncmp() handles this case fine and it already has been while
being lucky with what lim2 was [un]initialized as.

Reviewed by:	markj, Don Morris <dgmorris AT earthlink.net>
Sponsored by:	Dell EMC
Differential Revision:	https://reviews.freebsd.org/D27671
This commit is contained in:
Bryan Drewery 2020-12-18 09:58:03 -08:00
parent 556fcdce5b
commit f222a6b886
2 changed files with 8 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
sys/cddl/contrib/opensolaris/uts/common/dtrace/dtrace.c
View File

@ -6374,6 +6374,14 @@ dtrace_dif_emulate(dtrace_difo_t *difo, dtrace_mstate_t *mstate,
uintptr_t s2 = regs[r2];
size_t lim1, lim2;
/*
* If one of the strings is NULL then the limit becomes
* 0 which compares 0 characters in dtrace_strncmp()
* resulting in a false positive. dtrace_strncmp()
* treats a NULL as an empty 1-char string.
*/
lim1 = lim2 = 1;
if (s1 != 0 &&
!dtrace_strcanload(s1, sz, &lim1, mstate, vstate))
break;

1
sys/modules/dtrace/dtrace/Makefile
View File

@ -61,6 +61,5 @@ CFLAGS+= -include ${SYSDIR}/cddl/compat/opensolaris/sys/debug_compat.h
CFLAGS.dtrace_asm.S+= -D_SYS_ERRNO_H_ -D_SYS_PARAM_H_ -DLOCORE
CWARNFLAGS+= ${OPENZFS_CWARNFLAGS}
CWARNFLAGS+= -Wno-parentheses
CWARNFLAGS+= -Wno-uninitialized
CWARNFLAGS+= -Wno-cast-qual
CWARNFLAGS+= -Wno-unused