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coredump: Use the vma snapshot in fill_files_note

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Matthew Wilcox reported that there is a missing mmap_lock in
file_files_note that could possibly lead to a user after free.

Solve this by using the existing vma snapshot for consistency
and to avoid the need to take the mmap_lock anywhere in the
coredump code except for dump_vma_snapshot.

Update the dump_vma_snapshot to capture vm_pgoff and vm_file
that are neeeded by fill_files_note.

Add free_vma_snapshot to free the captured values of vm_file.

Reported-by: Matthew Wilcox <willy@infradead.org>
Link: https://lkml.kernel.org/r/20220131153740.2396974-1-willy@infradead.org
Cc: stable@vger.kernel.org
Fixes: a07279c9a8 ("binfmt_elf, binfmt_elf_fdpic: use a VMA list snapshot")
Fixes: 2aa362c49c ("coredump: extend core dump note section to contain file names of mapped files")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2022-03-08 13:04:19 -06:00
parent 9ec7d32307
commit 390031c942
3 changed files with 35 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
fs/binfmt_elf.c
View File

@ -1641,17 +1641,16 @@ static void fill_siginfo_note(struct memelfnote *note, user_siginfo_t *csigdata,
* long file_ofs
* followed by COUNT filenames in ASCII: "FILE1" NUL "FILE2" NUL...
*/
static int fill_files_note(struct memelfnote *note)
static int fill_files_note(struct memelfnote *note, struct coredump_params *cprm)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
unsigned count, size, names_ofs, remaining, n;
user_long_t *data;
user_long_t *start_end_ofs;
char *name_base, *name_curpos;
int i;
/* *Estimated* file count and total data size needed */
count = mm->map_count;
count = cprm->vma_count;
if (count > UINT_MAX / 64)
return -EINVAL;
size = count * 64;
@ -1673,11 +1672,12 @@ static int fill_files_note(struct memelfnote *note)
name_base = name_curpos = ((char *)data) + names_ofs;
remaining = size - names_ofs;
count = 0;
for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
for (i = 0; i < cprm->vma_count; i++) {
struct core_vma_metadata *m = &cprm->vma_meta[i];
struct file *file;
const char *filename;
file = vma->vm_file;
file = m->file;
if (!file)
continue;
filename = file_path(file, name_curpos, remaining);
@ -1697,9 +1697,9 @@ static int fill_files_note(struct memelfnote *note)
memmove(name_curpos, filename, n);
name_curpos += n;
*start_end_ofs++ = vma->vm_start;
*start_end_ofs++ = vma->vm_end;
*start_end_ofs++ = vma->vm_pgoff;
*start_end_ofs++ = m->start;
*start_end_ofs++ = m->end;
*start_end_ofs++ = m->pgoff;
count++;
}
@ -1710,7 +1710,7 @@ static int fill_files_note(struct memelfnote *note)
* Count usually is less than mm->map_count,
* we need to move filenames down.
*/
n = mm->map_count - count;
n = cprm->vma_count - count;
if (n != 0) {
unsigned shift_bytes = n * 3 * sizeof(data[0]);
memmove(name_base - shift_bytes, name_base,
@ -1909,7 +1909,7 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
fill_auxv_note(&info->auxv, current->mm);
info->size += notesize(&info->auxv);
if (fill_files_note(&info->files) == 0)
if (fill_files_note(&info->files, cprm) == 0)
info->size += notesize(&info->files);
return 1;
@ -2098,7 +2098,7 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
fill_auxv_note(info->notes + 3, current->mm);
info->numnote = 4;
if (fill_files_note(info->notes + info->numnote) == 0) {
if (fill_files_note(info->notes + info->numnote, cprm) == 0) {
info->notes_files = info->notes + info->numnote;
info->numnote++;
}

22
fs/coredump.c
View File

@ -55,6 +55,7 @@
#include <trace/events/sched.h>
static bool dump_vma_snapshot(struct coredump_params *cprm);
static void free_vma_snapshot(struct coredump_params *cprm);
static int core_uses_pid;
static unsigned int core_pipe_limit;
@ -765,7 +766,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
dump_emit(&cprm, "", 1);
}
file_end_write(cprm.file);
kvfree(cprm.vma_meta);
free_vma_snapshot(&cprm);
}
if (ispipe && core_pipe_limit)
wait_for_dump_helpers(cprm.file);
@ -1099,6 +1100,20 @@ static struct vm_area_struct *next_vma(struct vm_area_struct *this_vma,
return gate_vma;
}
static void free_vma_snapshot(struct coredump_params *cprm)
{
if (cprm->vma_meta) {
int i;
for (i = 0; i < cprm->vma_count; i++) {
struct file *file = cprm->vma_meta[i].file;
if (file)
fput(file);
}
kvfree(cprm->vma_meta);
cprm->vma_meta = NULL;
}
}
/*
* Under the mmap_lock, take a snapshot of relevant information about the task's
* VMAs.
@ -1135,6 +1150,11 @@ static bool dump_vma_snapshot(struct coredump_params *cprm)
m->end = vma->vm_end;
m->flags = vma->vm_flags;
m->dump_size = vma_dump_size(vma, cprm->mm_flags);
m->pgoff = vma->vm_pgoff;
m->file = vma->vm_file;
if (m->file)
get_file(m->file);
}
mmap_write_unlock(mm);

2
include/linux/coredump.h
View File

@ -12,6 +12,8 @@ struct core_vma_metadata {
unsigned long start, end;
unsigned long flags;
unsigned long dump_size;
unsigned long pgoff;
struct file *file;
};
struct coredump_params {