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coredump masking: reimplementation of dumpable using two flags

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This patch changes mm_struct.dumpable to a pair of bit flags.

set_dumpable() converts three-value dumpable to two flags and stores it into
lower two bits of mm_struct.flags instead of mm_struct.dumpable.
get_dumpable() behaves in the opposite way.

[[email protected]: export set_dumpable]
Signed-off-by: Hidehiro Kawai <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: David Howells <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Kawai, Hidehiro 2007-07-19 01:48:27 -07:00 • committed by Linus Torvalds
commit 6c5d523826
8 changed files with 82 additions and 25 deletions
Download patch file Download diff file Expand all files Collapse all files

62
fs/exec.c
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@ -1058,9 +1058,9 @@ int flush_old_exec(struct linux_binprm * bprm)
current->sas_ss_sp = current->sas_ss_size = 0;
if (current->euid == current->uid && current->egid == current->gid)
current->mm->dumpable = 1;
set_dumpable(current->mm, 1);
else
current->mm->dumpable = suid_dumpable;
set_dumpable(current->mm, suid_dumpable);
name = bprm->filename;
@ -1088,7 +1088,7 @@ int flush_old_exec(struct linux_binprm * bprm)
file_permission(bprm->file, MAY_READ) ||
(bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)) {
suid_keys(current);
current->mm->dumpable = suid_dumpable;
set_dumpable(current->mm, suid_dumpable);
}
/* An exec changes our domain. We are no longer part of the thread
@ -1665,6 +1665,56 @@ fail:
return core_waiters;
}
/*
* set_dumpable converts traditional three-value dumpable to two flags and
* stores them into mm->flags. It modifies lower two bits of mm->flags, but
* these bits are not changed atomically. So get_dumpable can observe the
* intermediate state. To avoid doing unexpected behavior, get get_dumpable
* return either old dumpable or new one by paying attention to the order of
* modifying the bits.
*
* dumpable | mm->flags (binary)
* old new | initial interim final
* ---------+-----------------------
* 0 1 | 00 01 01
* 0 2 | 00 10(*) 11
* 1 0 | 01 00 00
* 1 2 | 01 11 11
* 2 0 | 11 10(*) 00
* 2 1 | 11 11 01
*
* (*) get_dumpable regards interim value of 10 as 11.
*/
void set_dumpable(struct mm_struct *mm, int value)
{
switch (value) {
case 0:
clear_bit(MMF_DUMPABLE, &mm->flags);
smp_wmb();
clear_bit(MMF_DUMP_SECURELY, &mm->flags);
break;
case 1:
set_bit(MMF_DUMPABLE, &mm->flags);
smp_wmb();
clear_bit(MMF_DUMP_SECURELY, &mm->flags);
break;
case 2:
set_bit(MMF_DUMP_SECURELY, &mm->flags);
smp_wmb();
set_bit(MMF_DUMPABLE, &mm->flags);
break;
}
}
EXPORT_SYMBOL_GPL(set_dumpable);
int get_dumpable(struct mm_struct *mm)
{
int ret;
ret = mm->flags & 0x3;
return (ret >= 2) ? 2 : ret;
}
int do_coredump(long signr, int exit_code, struct pt_regs * regs)
{
char corename[CORENAME_MAX_SIZE + 1];
@ -1683,7 +1733,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
if (!binfmt || !binfmt->core_dump)
goto fail;
down_write(&mm->mmap_sem);
if (!mm->dumpable) {
if (!get_dumpable(mm)) {
up_write(&mm->mmap_sem);
goto fail;
}
@ -1693,11 +1743,11 @@ int 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 (mm->dumpable == 2) { /* Setuid core dump mode */
if (get_dumpable(mm) == 2) { /* Setuid core dump mode */
flag = O_EXCL; /* Stop rewrite attacks */
current->fsuid = 0; /* Dump root private */
}
mm->dumpable = 0;
set_dumpable(mm, 0);
retval = coredump_wait(exit_code);
if (retval < 0)