coredump: pass mm->flags as a coredump parameter for consistency

Pass mm->flags as a coredump parameter for consistency.

 ---
1787         if (mm->core_state || !get_dumpable(mm)) {  <- (1)
1788                 up_write(&mm->mmap_sem);
1789                 put_cred(cred);
1790                 goto fail;
1791         }
1792
[...]
1798         if (get_dumpable(mm) == 2) {    /* Setuid core dump mode */ <-(2)
1799                 flag = O_EXCL;          /* Stop rewrite attacks */
1800                 cred->fsuid = 0;        /* Dump root private */
1801         }
 ---

Since dumpable bits are not protected by lock, there is a chance to change
these bits between (1) and (2).

To solve this issue, this patch copies mm->flags to
coredump_params.mm_flags at the beginning of do_coredump() and uses it
instead of get_dumpable() while dumping core.

This copy is also passed to binfmt->core_dump, since elf*_core_dump() uses
dump_filter bits in mm->flags.

[akpm@linux-foundation.org: fix merge]
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 22 insertions, 26 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 78de530cfb02..535e763ab1a6 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1882,7 +1882,6 @@ 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;
-        unsigned long mm_flags;
         struct elf_note_info info;
         struct elf_phdr *phdr4note = NULL;
         struct elf_shdr *shdr4extnum = NULL;
@@ -1957,14 +1956,7 @@ static int elf_core_dump(struct coredump_params *cprm)
 
         dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);
 
-        /*
-         * We must use the same mm->flags while dumping core to avoid
-         * inconsistency between the program headers and bodies, otherwise an
-         * unusable core file can be generated.
-         */
-        mm_flags = current->mm->flags;
-
-        offset += elf_core_vma_data_size(gate_vma, mm_flags);
+        offset += elf_core_vma_data_size(gate_vma, cprm->mm_flags);
         offset += elf_core_extra_data_size();
         e_shoff = offset;
 
@@ -1995,7 +1987,7 @@ static int elf_core_dump(struct coredump_params *cprm)
                 phdr.p_offset = offset;
                 phdr.p_vaddr = vma->vm_start;
                 phdr.p_paddr = 0;
-                phdr.p_filesz = vma_dump_size(vma, mm_flags);
+                phdr.p_filesz = vma_dump_size(vma, cprm->mm_flags);
                 phdr.p_memsz = vma->vm_end - vma->vm_start;
                 offset += phdr.p_filesz;
                 phdr.p_flags = vma->vm_flags & VM_READ ? PF_R : 0;
@@ -2030,7 +2022,7 @@ static int elf_core_dump(struct coredump_params *cprm)
                 unsigned long addr;
                 unsigned long end;
 
-                end = vma->vm_start + vma_dump_size(vma, mm_flags);
+                end = vma->vm_start + vma_dump_size(vma, cprm->mm_flags);
 
                 for (addr = vma->vm_start; addr < end; addr += PAGE_SIZE) {
                         struct page *page;
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index e49d9c06a4b6..6d6a16c5e9bb 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1626,7 +1626,6 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 #endif
         int thread_status_size = 0;
         elf_addr_t *auxv;
-        unsigned long mm_flags;
         struct elf_phdr *phdr4note = NULL;
         struct elf_shdr *shdr4extnum = NULL;
         Elf_Half e_phnum;
@@ -1769,14 +1768,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
         /* Page-align dumped data */
         dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);
 
-        /*
-         * We must use the same mm->flags while dumping core to avoid
-         * inconsistency between the program headers and bodies, otherwise an
-         * unusable core file can be generated.
-         */
-        mm_flags = current->mm->flags;
-
-        offset += elf_core_vma_data_size(mm_flags);
+        offset += elf_core_vma_data_size(cprm->mm_flags);
         offset += elf_core_extra_data_size();
         e_shoff = offset;
 
@@ -1809,7 +1801,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
                 phdr.p_offset = offset;
                 phdr.p_vaddr = vma->vm_start;
                 phdr.p_paddr = 0;
-                phdr.p_filesz = maydump(vma, mm_flags) ? sz : 0;
+                phdr.p_filesz = maydump(vma, cprm->mm_flags) ? sz : 0;
                 phdr.p_memsz = sz;
                 offset += phdr.p_filesz;
                 phdr.p_flags = vma->vm_flags & VM_READ ? PF_R : 0;
@@ -1847,7 +1839,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
                 goto end_coredump;
 
         if (elf_fdpic_dump_segments(cprm->file, &size, &cprm->limit,
-                                    mm_flags) < 0)
+                                    cprm->mm_flags) < 0)
                 goto end_coredump;
 
         if (!elf_core_write_extra_data(cprm->file, &size, cprm->limit))
diff --git a/fs/exec.c b/fs/exec.c
index da2b31dc4e1c..89d4080c1435 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1748,14 +1748,19 @@ void set_dumpable(struct mm_struct *mm, int value)
         }
 }
 
-int get_dumpable(struct mm_struct *mm)
+static int __get_dumpable(unsigned long mm_flags)
 {
         int ret;
 
-        ret = mm->flags & 0x3;
+        ret = mm_flags & MMF_DUMPABLE_MASK;
         return (ret >= 2) ? 2 : ret;
 }
 
+int get_dumpable(struct mm_struct *mm)
+{
+        return __get_dumpable(mm->flags);
+}
+
 static void wait_for_dump_helpers(struct file *file)
 {
         struct pipe_inode_info *pipe;
@@ -1799,6 +1804,12 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
                 .signr = signr,
                 .regs = regs,
                 .limit = rlimit(RLIMIT_CORE),
+                /*
+                 * We must use the same mm->flags while dumping core to avoid
+                 * inconsistency of bit flags, since this flag is not protected
+                 * by any locks.
+                 */
+                .mm_flags = mm->flags,
         };
 
         audit_core_dumps(signr);
@@ -1817,7 +1828,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
         /*
          * If another thread got here first, or we are not dumpable, bail out.
          */
-        if (mm->core_state || !get_dumpable(mm)) {
+        if (mm->core_state || !__get_dumpable(cprm.mm_flags)) {
                 up_write(&mm->mmap_sem);
                 put_cred(cred);
                 goto fail;
@@ -1828,7 +1839,8 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
          *      process nor do we know its entire history. We only know it
          *      was tainted so we dump it as root in mode 2.
          */
-        if (get_dumpable(mm) == 2) {    /* Setuid core dump mode */
+        if (__get_dumpable(cprm.mm_flags) == 2) {
+                /* Setuid core dump mode */
                 flag = O_EXCL;          /* Stop rewrite attacks */
                 cred->fsuid = 0;        /* Dump root private */
         }