On Tue, May 28, 2019 at 01:11:42PM +0800, Paul Wise wrote: > Save the offsets of the start of each argument to avoid having to > update pointers to each argument after every corename krealloc and > to avoid having to duplicate the memory for the dump command. > > Executable names containing spaces were previously being expanded from > %e or %E and then split in the middle of the filename. This is incorrect > behaviour since an argument list can represent arguments with spaces. > > The splitting could lead to extra arguments being passed to the core dump > handler that it might have interpreted as options or ignored completely. > > Core dump handlers that are not aware of this Linux kernel issue will be > using %e or %E without considering that it may be split and so they will > be vulnerable to processes with spaces in their names breaking their > argument list. If their internals are otherwise well written, such as > if they are written in shell but quote arguments, they will work better > after this change than before. If they are not well written, then there > is a slight chance of breakage depending on the details of the code but > they will already be fairly broken by the split filenames. > > Core dump handlers that are aware of this Linux kernel issue will be > placing %e or %E as the last item in their core_pattern and then > aggregating all of the remaining arguments into one, separated by > spaces. Alternatively they will be obtaining the filename via other > methods. Both of these will be compatible with the new arrangement. > > A side effect from this change is that unknown template types > (for example %z) result in an empty argument to the dump handler > instead of the argument being dropped. This is a desired change as: > > It is easier for dump handlers to process empty arguments than dropped > ones, especially if they are written in shell or don't pass each template > item with a preceding command-line option in order to differentiate > between individual template types. Most core_patterns in the wild do not > use options so they can confuse different template types (especially > numeric ones) if an earlier one gets dropped in old kernels. If the > kernel introduces a new template type and a core_pattern uses it, the > core dump handler might not expect that the argument can be dropped in > old kernels. > > For example, this can result in security issues when %d is dropped in old > kernels. This happened with the corekeeper package in Debian and resulted > in the interface between corekeeper and Linux having to be rewritten to > use command-line options to differentiate between template types. > > The core_pattern for most core dump handlers is written by the handler > author who would generally not insert unknown template types so this > change should be compatible with all the core dump handlers that exist. > > Fixes: 74aadce98605 > Reported-by: Jakub Wilk <jw...@jwilk.net> > Reported-in: https://bugs.debian.org/924398 > Reported-by: Paul Wise <pa...@bonedaddy.net> > Reported-in: > https://lore.kernel.org/linux-fsdevel/c8b7ecb8508895bf4adb62a748e2ea2c71854597.ca...@bonedaddy.net/ > Suggested-by: Jakub Wilk <jw...@jwilk.net> > Signed-off-by: Paul Wise <pa...@bonedaddy.net> > --- > fs/coredump.c | 44 +++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 39 insertions(+), 5 deletions(-) > > Changelog: > v3 Adjust footer fields, drop obvious comment > v2 Fix build failure due to typo after variable renaming > > diff --git a/fs/coredump.c b/fs/coredump.c > index e42e17e55bfd..b1ea7dfbd149 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -7,6 +7,7 @@ > #include <linux/stat.h> > #include <linux/fcntl.h> > #include <linux/swap.h> > +#include <linux/ctype.h> > #include <linux/string.h> > #include <linux/init.h> > #include <linux/pagemap.h> > @@ -187,11 +188,13 @@ static int cn_print_exe_file(struct core_name *cn) > * name into corename, which must have space for at least > * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator. > */ > -static int format_corename(struct core_name *cn, struct coredump_params > *cprm) > +static int format_corename(struct core_name *cn, struct coredump_params > *cprm, > + size_t **argv, int *argc) > { > const struct cred *cred = current_cred(); > const char *pat_ptr = core_pattern; > int ispipe = (*pat_ptr == '|'); > + bool was_space = false; > int pid_in_pattern = 0; > int err = 0; > > @@ -201,12 +204,35 @@ static int format_corename(struct core_name *cn, struct > coredump_params *cprm) > return -ENOMEM; > cn->corename[0] = '\0'; > > - if (ispipe) > + if (ispipe) { > + int argvs = sizeof(core_pattern) / 2; > + (*argv) = kmalloc_array(argvs, sizeof(**argv), GFP_KERNEL); > + if (!(*argv)) > + return -ENOMEM; > + (*argv)[(*argc)++] = 0; > ++pat_ptr; > + } > > /* Repeat as long as we have more pattern to process and more output > space */ > while (*pat_ptr) { > + /* > + * Split on spaces before doing template expansion so that > + * %e and %E don't get split if they have spaces in them > + */ > + if (ispipe) { > + if (isspace(*pat_ptr)) { > + was_space = true; > + pat_ptr++; > + continue; > + } else if (was_space) { > + was_space = false; > + err = cn_printf(cn, "%c", '\0'); > + if (err) > + return err; > + (*argv)[(*argc)++] = cn->used; > + } > + } > if (*pat_ptr != '%') { > err = cn_printf(cn, "%c", *pat_ptr++); > } else { > @@ -546,6 +572,8 @@ void do_coredump(const kernel_siginfo_t *siginfo) > struct cred *cred; > int retval = 0; > int ispipe; > + size_t *argv = NULL; > + int argc = 0; > struct files_struct *displaced; > /* require nonrelative corefile path and be extra careful */ > bool need_suid_safe = false; > @@ -592,9 +620,10 @@ void do_coredump(const kernel_siginfo_t *siginfo) > > old_cred = override_creds(cred); > > - ispipe = format_corename(&cn, &cprm); > + ispipe = format_corename(&cn, &cprm, &argv, &argc); > > if (ispipe) { > + int argi; > int dump_count; > char **helper_argv; > struct subprocess_info *sub_info; > @@ -637,12 +666,16 @@ void do_coredump(const kernel_siginfo_t *siginfo) > goto fail_dropcount; > } > > - helper_argv = argv_split(GFP_KERNEL, cn.corename, NULL); > + helper_argv = kmalloc_array(argc + 1, sizeof(*helper_argv), > + GFP_KERNEL); > if (!helper_argv) { > printk(KERN_WARNING "%s failed to allocate memory\n", > __func__); > goto fail_dropcount; > } > + for (argi = 0; argi < argc; argi++) > + helper_argv[argi] = cn.corename + argv[argi]; > + helper_argv[argi] = NULL; > > retval = -ENOMEM; > sub_info = call_usermodehelper_setup(helper_argv[0], > @@ -652,7 +685,7 @@ void do_coredump(const kernel_siginfo_t *siginfo) > retval = call_usermodehelper_exec(sub_info, > UMH_WAIT_EXEC); > > - argv_free(helper_argv); > + kfree(helper_argv); > if (retval) { > printk(KERN_INFO "Core dump to |%s pipe failed\n", > cn.corename); > @@ -766,6 +799,7 @@ void do_coredump(const kernel_siginfo_t *siginfo) > if (ispipe) > atomic_dec(&core_dump_count); > fail_unlock: > + kfree(argv); > kfree(cn.corename); > coredump_finish(mm, core_dumped); > revert_creds(old_cred); > -- > 2.20.1 > > Acked-by: Neil Horman <nhor...@tuxdriver.com>
