[PATCH v3 3/7] trace2: remove use of xstrdup()

From: Derrick Stolee <stolee@gmail.com>

In the previous change, we removed a use of xsprintf() that caused a recursive die() loop when failing to allocate memory. The trace2 library is too low-level to be calling die(), especially because of these recursive loops that can occur during the die handler.

For full defense in depth, we remove the xstrdup() calls from trace2/tr2_sysenv.c.

First, in tr2_sysenv_cb(), we need to handle a failed assignment of the value with a zero-valued return to halt the config parsing loop. Note that we don't want to use a negative return here or we would imply to the config system that the config key or value was somehow invalid; such an output would mask the real issue that the process failed to allocate memory.

Second, in tr2_sysenv_get(), the method will return NULL when strdup() returns NULL. This return is indistinguishable from the environment variable having no value. That means that all callers know how to handle a NULL response, but no behavior change will occur between the case of no environment being set and detecting an environment variable exists but we fail to duplicate it. This seems an appropriate trade-off, as an allocation failure at this level will likely lead to failure in another system, but at least the trace2 API will not cause the process to fail early.

Helped-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 banned-die.h        | 3 +++
 trace2/tr2_sysenv.c | 6 ++++--
 2 files changed, 7 insertions(+), 2 deletions(-)