----- On Mar 14, 2017, at 10:37 AM, Jonathan Rajotte [email protected] wrote:
> v2: merged previous series in one patch since the second patch is a minor fix > and partly addressed in the first patch. > > "start" -> starts > > -- > > fscanf on an empty file returns directly without assigning value to > 'index' leading to assigning the value of an uninitialized variable to > syscall_table_nb_entry. This can result in memory allocation problems > when listing syscalls on 'lttng list --kernel --syscall'[1][2]. > > Fixes at the same time an off-by-one problem for the index > value. Fixing this off-by-one also fixes the missing last element issue. It should be described in this changelog, but it's not. Only the effect on memory allocation is discussed. Thanks, Mathieu > > The index value returned by fscanf is an index starting at 0. > However, it is later used to count how many elements need to be > allocated, without any extra increment. > > It does not cause issues in practice because SYSCALL_TABLE_INIT_SIZE > is nonzero, and because we don't require the table to expand by more > than the double of its size at once (which could happen if we could > have a hole in the syscall table for instance). > > It's better to fix this off-by-one for clarity, and in case this code > gets re-used in other contexts that don't have the same memory growth > pattern. > > Fixes #1091 > > [1] https://bugs.lttng.org/issues/1091 > [2] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1671063/ > > Signed-off-by: Jonathan Rajotte <[email protected]> > --- > src/bin/lttng-sessiond/syscall.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/src/bin/lttng-sessiond/syscall.c > b/src/bin/lttng-sessiond/syscall.c > index 6ee38bd..7d0a92b 100644 > --- a/src/bin/lttng-sessiond/syscall.c > +++ b/src/bin/lttng-sessiond/syscall.c > @@ -16,6 +16,8 @@ > */ > > #define _LGPL_SOURCE > +#include <stdbool.h> > + > #include <common/bitfield.h> > #include <common/common.h> > #include <common/kernel-ctl/kernel-ctl.h> > @@ -43,7 +45,8 @@ int syscall_init_table(void) > size_t nbmem; > FILE *fp; > /* Syscall data from the kernel. */ > - size_t index; > + size_t index = 0; > + bool at_least_one_syscall = false; > uint32_t bitness; > char name[SYSCALL_NAME_LEN]; > > @@ -76,12 +79,13 @@ int syscall_init_table(void) > name = %" XSTR(SYSCALL_NAME_LEN) "[^;]; \ > bitness = %u; };\n", > &index, name, &bitness) == 3) { > - if (index >= nbmem ) { > + at_least_one_syscall = true; > + if (index >= nbmem) { > struct syscall *new_list; > size_t new_nbmem; > > /* Double memory size. */ > - new_nbmem = max(index, nbmem << 1); > + new_nbmem = max(index + 1, nbmem << 1); > if (new_nbmem > (SIZE_MAX / sizeof(*new_list))) { > /* Overflow, stop everything, something went > really wrong. */ > ERR("Syscall listing memory size overflow. > Stopping"); > @@ -123,7 +127,10 @@ int syscall_init_table(void) > */ > } > > - syscall_table_nb_entry = index; > + /* Index starts at 0. */ > + if (at_least_one_syscall) { > + syscall_table_nb_entry = index + 1; > + } > > ret = 0; > > -- > 2.7.4 > > _______________________________________________ > lttng-dev mailing list > [email protected] > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
