Commit 6c5d5238 authored by Kawai, Hidehiro's avatar Kawai, Hidehiro Committed by Linus Torvalds
Browse files

coredump masking: reimplementation of dumpable using two flags 



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.

[akpm@linux-foundation.org: export set_dumpable]
Signed-off-by: default avatarHidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 76fdbb25

fs/exec.c

+56 −6
Original line number Diff line number Diff line
@@ -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)

fs/proc/base.c

+1 −1
Original line number Diff line number Diff line
@@ -1014,7 +1014,7 @@ static int task_dumpable(struct task_struct *task) 
	task_lock(task);

	mm = task->mm;

	if (mm)

		dumpable = mm->dumpable;

		dumpable = get_dumpable(mm);

	task_unlock(task);

	if(dumpable == 1)

		return 1;

include/asm-ia64/processor.h

+2 −2
Original line number Diff line number Diff line
@@ -295,9 +295,9 @@ struct thread_struct { 
	regs->ar_bspstore = current->thread.rbs_bot;						\

	regs->ar_fpsr = FPSR_DEFAULT;								\

	regs->loadrs = 0;									\

	regs->r8 = current->mm->dumpable;	/* set "don't zap registers" flag */		\

	regs->r8 = get_dumpable(current->mm);	/* set "don't zap registers" flag */		\

	regs->r12 = new_sp - 16;	/* allocate 16 byte scratch area */			\

	if (unlikely(!current->mm->dumpable)) {							\

	if (unlikely(!get_dumpable(current->mm))) {							\

		/*										\

		 * Zap scratch regs to avoid leaking bits between processes with different	\

		 * uid/privileges.								\

include/linux/sched.h

+8 −1
Original line number Diff line number Diff line
@@ -345,6 +345,13 @@ typedef unsigned long mm_counter_t; 
		(mm)->hiwater_vm = (mm)->total_vm;	\

} while (0)



extern void set_dumpable(struct mm_struct *mm, int value);

extern int get_dumpable(struct mm_struct *mm);



/* mm flags */

#define MMF_DUMPABLE      0  /* core dump is permitted */

#define MMF_DUMP_SECURELY 1  /* core file is readable only by root */



struct mm_struct {

	struct vm_area_struct * mmap;		/* list of VMAs */

	struct rb_root mm_rb;
@@ -402,7 +409,7 @@ struct mm_struct { 
	unsigned int token_priority;

	unsigned int last_interval;



	unsigned char dumpable:2;

	unsigned long flags; /* Must use atomic bitops to access the bits */



	/* coredumping support */

	int core_waiters;

kernel/ptrace.c

+1 −1
Original line number Diff line number Diff line
@@ -142,7 +142,7 @@ static int may_attach(struct task_struct *task) 
		return -EPERM;

	smp_rmb();

	if (task->mm)

		dumpable = task->mm->dumpable;

		dumpable = get_dumpable(task->mm);

	if (!dumpable && !capable(CAP_SYS_PTRACE))

		return -EPERM;

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