fs/binfmt_elf.c: prevent a coredump with a large vm_map_count from Oopsing

A high setting of max_map_count, and a process core-dumping with a large
enough vm_map_count could result in an NT_FILE note not being written,
and the kernel crashing immediately later because it has assumed
otherwise.

Reproduction of the oops-causing bug described here:

    https://lkml.org/lkml/2013/8/30/50

Rge ussue originated in commit 2aa362c49c31 ("coredump: extend core dump
note section to contain file names of mapped file") from Oct 4, 2012.

This patch make that section optional in that case.  fill_files_note()
should signify the error, and also let the info struct in
elf_core_dump() be zero-initialized so that we can check for the
optionally written note.

[akpm@linux-foundation.org: avoid abusing E2BIG, remove a couple of not-really-needed local variables]
[akpm@linux-foundation.org: fix sparse warning]
Signed-off-by: Dan Aloni <alonid@stratoscale.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Reported-by: Martin MOKREJS <mmokrejs@gmail.com>
Tested-by: Martin MOKREJS <mmokrejs@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 12 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 100edcc5e312..4c94a79991bb 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1413,7 +1413,7 @@ 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 void fill_files_note(struct memelfnote *note)
+static int fill_files_note(struct memelfnote *note)
 {
         struct vm_area_struct *vma;
         unsigned count, size, names_ofs, remaining, n;
@@ -1428,11 +1428,11 @@ static void fill_files_note(struct memelfnote *note)
         names_ofs = (2 + 3 * count) * sizeof(data[0]);
  alloc:
         if (size >= MAX_FILE_NOTE_SIZE) /* paranoia check */
-                goto err;
+                return -EINVAL;
         size = round_up(size, PAGE_SIZE);
         data = vmalloc(size);
         if (!data)
-                goto err;
+                return -ENOMEM;
 
         start_end_ofs = data + 2;
         name_base = name_curpos = ((char *)data) + names_ofs;
@@ -1485,7 +1485,7 @@ static void fill_files_note(struct memelfnote *note)
 
         size = name_curpos - (char *)data;
         fill_note(note, "CORE", NT_FILE, size, data);
- err: ;
+        return 0;
 }
 
 #ifdef CORE_DUMP_USE_REGSET
@@ -1686,8 +1686,8 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
         fill_auxv_note(&info->auxv, current->mm);
         info->size += notesize(&info->auxv);
 
-        fill_files_note(&info->files);
-        info->size += notesize(&info->files);
+        if (fill_files_note(&info->files) == 0)
+                info->size += notesize(&info->files);
 
         return 1;
 }
@@ -1719,7 +1719,8 @@ static int write_note_info(struct elf_note_info *info,
                         return 0;
                 if (first && !writenote(&info->auxv, file, foffset))
                         return 0;
-                if (first && !writenote(&info->files, file, foffset))
+                if (first && info->files.data &&
+                                !writenote(&info->files, file, foffset))
                         return 0;
 
                 for (i = 1; i < info->thread_notes; ++i)
@@ -1806,6 +1807,7 @@ static int elf_dump_thread_status(long signr, struct elf_thread_status *t)
 
 struct elf_note_info {
         struct memelfnote *notes;
+        struct memelfnote *notes_files;
         struct elf_prstatus *prstatus;  /* NT_PRSTATUS */
         struct elf_prpsinfo *psinfo;    /* NT_PRPSINFO */
         struct list_head thread_list;
@@ -1896,9 +1898,12 @@ static int fill_note_info(struct elfhdr *elf, int phdrs,
 
         fill_siginfo_note(info->notes + 2, &info->csigdata, siginfo);
         fill_auxv_note(info->notes + 3, current->mm);
-        fill_files_note(info->notes + 4);
+        info->numnote = 4;
 
-        info->numnote = 5;
+        if (fill_files_note(info->notes + info->numnote) == 0) {
+                info->notes_files = info->notes + info->numnote;
+                info->numnote++;
+        }
 
         /* Try to dump the FPU. */
         info->prstatus->pr_fpvalid = elf_core_copy_task_fpregs(current, regs,
@@ -1960,8 +1965,9 @@ static void free_note_info(struct elf_note_info *info)
                 kfree(list_entry(tmp, struct elf_thread_status, list));
         }
 
-        /* Free data allocated by fill_files_note(): */
-        vfree(info->notes[4].data);
+        /* Free data possibly allocated by fill_files_note(): */
+        if (info->notes_files)
+                vfree(info->notes_files->data);
 
         kfree(info->prstatus);
         kfree(info->psinfo);
@@ -2044,7 +2050,7 @@ static int elf_core_dump(struct coredump_params *cprm)
         struct vm_area_struct *vma, *gate_vma;
         struct elfhdr *elf = NULL;
         loff_t offset = 0, dataoff, foffset;
-        struct elf_note_info info;
+        struct elf_note_info info = { };
         struct elf_phdr *phdr4note = NULL;
         struct elf_shdr *shdr4extnum = NULL;
         Elf_Half e_phnum;