From 55ac995a979794ea3340973c6b320b64e1016177 Mon Sep 17 00:00:00 2001 From: Andrew Lukoshko Date: Fri, 15 May 2026 08:39:11 +0000 Subject: [PATCH] ptrace: slightly saner get_dumpable() logic Backport of upstream commit 31e62c2ebbfd ("ptrace: slightly saner 'get_dumpable()' logic") posted by Linus Torvalds in response to a Qualys Security Advisory. ptrace_may_access() no longer trusts an absent mm as 'dumpable enough'; mm-less targets (kernel threads, exited tasks) now require CAP_SYS_PTRACE. A new user_dumpable bit in task_struct caches the last user-dumpable state of a task whose mm has been torn down in exit_mm(). Applies to AlmaLinux 10s as-is (offset-only adjusted for the 227 source base, no fuzz). --- 1103-ptrace-saner-get_dumpable-logic.patch | 109 +++++++++++++++++++++ kernel.spec | 2 + 2 files changed, 111 insertions(+) create mode 100644 1103-ptrace-saner-get_dumpable-logic.patch diff --git a/1103-ptrace-saner-get_dumpable-logic.patch b/1103-ptrace-saner-get_dumpable-logic.patch new file mode 100644 index 000000000..f9e55362d --- /dev/null +++ b/1103-ptrace-saner-get_dumpable-logic.patch @@ -0,0 +1,109 @@ +From: Linus Torvalds +Subject: [PATCH AlmaLinux 10s] ptrace: slightly saner 'get_dumpable()' logic + +Backport of upstream commit 31e62c2ebbfd ("ptrace: slightly saner +'get_dumpable()' logic") posted at +https://github.com/torvalds/linux/commit/31e62c2ebbfdc3fe3dbdf5e02c92a9dc67087a3a + +The 'dumpability' of a task is fundamentally about the memory image of +the task -- the concept comes from whether it can core dump or not -- +and makes no sense when you don't have an associated mm. + +And almost all users do in fact use it only for the case where the +task has a mm pointer. + +But we have one odd special case: ptrace_may_access() uses 'dumpable' +to check various other things entirely independently of the MM +(typically explicitly using flags like PTRACE_MODE_READ_FSCREDS). +Including for threads that no longer have a VM (and maybe never did, +like most kernel threads). + +The ptrace code does check that the uid/gid matches, so you do have +to be uid-0 to see kernel thread details, but this means that the +traditional "drop capabilities" model doesn't make any difference +for this all. + +Make it all make a bit more sense by saying that if you don't have a +MM pointer, we use a cached "last dumpability" flag if the thread +ever had a MM (it will be zero for kernel threads since it is never +set), and require a proper CAP_SYS_PTRACE capability to override. + +Verified to apply with `patch -p1 -F0` (no offset, no fuzz, no rejects) +against kernel-6.12.0-227.el10. + +Reported-by: Qualys Security Advisory +Cc: Oleg Nesterov +Cc: Kees Cook +Signed-off-by: Linus Torvalds +--- + include/linux/sched.h | 3 +++ + kernel/exit.c | 1 + + kernel/ptrace.c | 22 ++++++++++++++++------ + 3 files changed, 20 insertions(+), 6 deletions(-) + +--- a/include/linux/sched.h ++++ b/include/linux/sched.h +@@ -1005,6 +1005,9 @@ struct task_struct { + unsigned sched_rt_mutex:1; + #endif + ++ /* Save user-dumpable when mm goes away */ ++ unsigned user_dumpable:1; ++ + /* Bit to tell TOMOYO we're in execve(): */ + unsigned in_execve:1; + unsigned in_iowait:1; +--- a/kernel/exit.c ++++ b/kernel/exit.c +@@ -563,6 +563,7 @@ static void exit_mm(void) + */ + smp_mb__after_spinlock(); + local_irq_disable(); ++ current->user_dumpable = (get_dumpable(mm) == SUID_DUMP_USER); + current->mm = NULL; + membarrier_update_current_mm(NULL); + enter_lazy_tlb(mm, current); +--- a/kernel/ptrace.c ++++ b/kernel/ptrace.c +@@ -272,11 +272,24 @@ static bool ptrace_has_cap(struct user_namespace *ns, unsigned int mode) + return ns_capable(ns, CAP_SYS_PTRACE); + } + ++static bool task_still_dumpable(struct task_struct *task, unsigned int mode) ++{ ++ struct mm_struct *mm = task->mm; ++ if (mm) { ++ if (get_dumpable(mm) == SUID_DUMP_USER) ++ return true; ++ return ptrace_has_cap(mm->user_ns, mode); ++ } ++ ++ if (task->user_dumpable) ++ return true; ++ return ptrace_has_cap(&init_user_ns, mode); ++} ++ + /* Returns 0 on success, -errno on denial. */ + static int __ptrace_may_access(struct task_struct *task, unsigned int mode) + { + const struct cred *cred = current_cred(), *tcred; +- struct mm_struct *mm; + kuid_t caller_uid; + kgid_t caller_gid; + +@@ -337,11 +350,8 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) + * Pairs with a write barrier in commit_creds(). + */ + smp_rmb(); +- mm = task->mm; +- if (mm && +- ((get_dumpable(mm) != SUID_DUMP_USER) && +- !ptrace_has_cap(mm->user_ns, mode))) +- return -EPERM; ++ if (!task_still_dumpable(task, mode)) ++ return -EPERM; + + return security_ptrace_access_check(task, mode); + } +-- +2.43.0 diff --git a/kernel.spec b/kernel.spec index 127ef3060..e82ad1764 100644 --- a/kernel.spec +++ b/kernel.spec @@ -1146,6 +1146,7 @@ Patch2010: 0001-Keep-fs-btrfs-files-in-modules-package.patch Patch1100: 1100-xfrm-esp-avoid-in-place-decrypt-shared-skb-frags.patch Patch1101: 1101-rxrpc-linearize-paged-frags.patch Patch1102: 1102-net-skbuff-propagate-shared-frag-marker.patch +Patch1103: 1103-ptrace-saner-get_dumpable-logic.patch # END OF PATCH DEFINITIONS @@ -2044,6 +2045,7 @@ ApplyPatch 0001-Keep-fs-btrfs-files-in-modules-package.patch ApplyPatch 1100-xfrm-esp-avoid-in-place-decrypt-shared-skb-frags.patch ApplyPatch 1101-rxrpc-linearize-paged-frags.patch ApplyPatch 1102-net-skbuff-propagate-shared-frag-marker.patch +ApplyPatch 1103-ptrace-saner-get_dumpable-logic.patch %{log_msg "End of patch applications"} # END OF PATCH APPLICATIONS