From: Liam R. Howlett Date: Wed, 14 Jun 2023 22:30:35 +0000 (-0400) Subject: mm/mmap: Fix use-after-free when expanding the VMA X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=refs%2Fheads%2Fv6.4-rc5_fixes;p=users%2Fjedix%2Flinux-maple.git mm/mmap: Fix use-after-free when expanding the VMA Expanding the VMA can cause new maple tree nodes to be used if a gap disappears, or the VMA expands beyond the node boundary into the preceding node (GROWSUP only). Since the expansion only takes the read lock and other readers are not taking the rcu read lock, other walkers may still have a pointer to the freed node. Fix the use-after-free by dropping the read lock and obtaining the write lock in these cases. In the case of GROWSUP, ensure the write lock is always taken. Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree") Cc: stable@vger.kernel.org Reported-and-tested-by: syzbot+f3728183b2f78d0d40f6@syzkaller.appspotmail.com Reported-by: Ruihan Li Co-Developed-by: Matthew Wilcox (Oracle) Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Liam R. Howlett --- diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index e4399983c50c..af686f6b35aa 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1237,6 +1237,7 @@ void do_user_addr_fault(struct pt_regs *regs, struct mm_struct *mm; vm_fault_t fault; unsigned int flags = FAULT_FLAG_DEFAULT; + int err; tsk = current; mm = tsk->mm; @@ -1405,11 +1406,16 @@ retry: } if (likely(vma->vm_start <= address)) goto good_area; - if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { - bad_area(regs, error_code, address); - return; + err = expand_stack(vma, address, false); + if (unlikely(err == -EAGAIN)) { + mmap_read_unlock(mm); + mmap_write_lock(mm); + vma = find_vma(mm, address); + if (vma) + err = expand_stack(vma, address, true); + mmap_write_downgrade(mm); } - if (unlikely(expand_stack(vma, address))) { + if (unlikely(err)) { bad_area(regs, error_code, address); return; } diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 1033fbdfdbec..869c3aa0e455 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -320,10 +320,10 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec, * Grow the stack manually; some architectures have a limit on how * far ahead a user-space access may be in order to grow the stack. */ - if (mmap_read_lock_killable(mm)) + if (mmap_write_lock_killable(mm)) return -EINTR; - vma = find_extend_vma(mm, bprm->p); - mmap_read_unlock(mm); + vma = find_extend_vma_locked(mm, bprm->p, true); + mmap_write_unlock(mm); if (!vma) return -EFAULT; diff --git a/fs/exec.c b/fs/exec.c index a466e797c8e2..9157b9c25631 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -205,9 +205,11 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, #ifdef CONFIG_STACK_GROWSUP if (write) { - ret = expand_downwards(bprm->vma, pos); + mmap_write_lock(bprm->mm); + ret = expand_downwards(bprm->vma, pos, true); if (ret < 0) return NULL; + mmap_write_unlock(bprm->mm); } #endif @@ -853,7 +855,7 @@ int setup_arg_pages(struct linux_binprm *bprm, stack_base = vma->vm_end - stack_expand; #endif current->mm->start_stack = bprm->p; - ret = expand_stack(vma, stack_base); + ret = expand_stack(vma, stack_base, true); if (ret) ret = -EFAULT; diff --git a/include/linux/mm.h b/include/linux/mm.h index 27ce77080c79..58826659c744 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3190,11 +3190,12 @@ extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); extern unsigned long stack_guard_gap; /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */ -extern int expand_stack(struct vm_area_struct *vma, unsigned long address); +int expand_stack(struct vm_area_struct *vma, unsigned long address, + bool write_locked); /* CONFIG_STACK_GROWSUP still needs to grow downwards at some places */ -extern int expand_downwards(struct vm_area_struct *vma, - unsigned long address); +int expand_downwards(struct vm_area_struct *vma, unsigned long address, + bool write_locked); #if VM_GROWSUP extern int expand_upwards(struct vm_area_struct *vma, unsigned long address); #else @@ -3295,6 +3296,8 @@ unsigned long change_prot_numa(struct vm_area_struct *vma, #endif struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr); +struct vm_area_struct *find_extend_vma_locked(struct mm_struct *, + unsigned long addr, bool write_locked); int remap_pfn_range(struct vm_area_struct *, unsigned long addr, unsigned long pfn, unsigned long size, pgprot_t); int remap_pfn_range_notrack(struct vm_area_struct *vma, unsigned long addr, diff --git a/mm/mmap.c b/mm/mmap.c index 13678edaa22c..2f560181148d 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1935,7 +1935,8 @@ static int acct_stack_growth(struct vm_area_struct *vma, * PA-RISC uses this for its stack; IA64 for its Register Backing Store. * vma is the last one with address > vma->vm_end. Have to extend vma. */ -int expand_upwards(struct vm_area_struct *vma, unsigned long address) +int expand_upwards(struct vm_area_struct *vma, unsigned long address, + bool write_locked) { struct mm_struct *mm = vma->vm_mm; struct vm_area_struct *next; @@ -1959,6 +1960,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) if (gap_addr < address || gap_addr > TASK_SIZE) gap_addr = TASK_SIZE; + if (!write_locked) + return -EAGAIN; next = find_vma_intersection(mm, vma->vm_end, gap_addr); if (next && vma_is_accessible(next)) { if (!(next->vm_flags & VM_GROWSUP)) @@ -2028,7 +2031,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address) /* * vma is the first one with address < vma->vm_start. Have to extend vma. */ -int expand_downwards(struct vm_area_struct *vma, unsigned long address) +int expand_downwards(struct vm_area_struct *vma, unsigned long address, + bool write_locked) { struct mm_struct *mm = vma->vm_mm; MA_STATE(mas, &mm->mm_mt, vma->vm_start, vma->vm_start); @@ -2042,10 +2046,13 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address) /* Enforce stack_guard_gap */ prev = mas_prev(&mas, 0); /* Check that both stack segments have the same anon_vma? */ - if (prev && !(prev->vm_flags & VM_GROWSDOWN) && - vma_is_accessible(prev)) { - if (address - prev->vm_end < stack_guard_gap) + if (prev) { + if (!(prev->vm_flags & VM_GROWSDOWN) && + vma_is_accessible(prev) && + (address - prev->vm_end < stack_guard_gap)) return -ENOMEM; + if (!write_locked && (prev->vm_end == address)) + return -EAGAIN; } if (mas_preallocate(&mas, GFP_KERNEL)) @@ -2124,37 +2131,59 @@ static int __init cmdline_parse_stack_guard_gap(char *p) __setup("stack_guard_gap=", cmdline_parse_stack_guard_gap); #ifdef CONFIG_STACK_GROWSUP -int expand_stack(struct vm_area_struct *vma, unsigned long address) +int expand_stack(struct vm_area_struct *vma, unsigned long address, + bool write_locked) { - return expand_upwards(vma, address); + return expand_upwards(vma, address, write_locked); } -struct vm_area_struct * -find_extend_vma(struct mm_struct *mm, unsigned long addr) +struct vm_area_struct *find_extend_vma_locked(struct mm_struct *mm, + unsigned long addr, bool write_locked) { struct vm_area_struct *vma, *prev; + int err; addr &= PAGE_MASK; vma = find_vma_prev(mm, addr, &prev); if (vma && (vma->vm_start <= addr)) return vma; - if (!prev || expand_stack(prev, addr)) + if (!prev) + return NULL; + if (write_locked) { + err = expand_stack(prev, addr, true); + } else { + mmap_read_unlock(mm); + mmap_write_lock(mm); + vma = find_vma_prev(mm, addr, &prev); + if (vma && (vma->vm_start <= addr)) { + mmap_write_downgrade(mm); + return vma; + } + if (prev) + err = expand_stack(prev, addr, true); + mmap_write_downgrade(mm); + } + if (err) return NULL; if (prev->vm_flags & VM_LOCKED) populate_vma_page_range(prev, addr, prev->vm_end, NULL); return prev; } #else -int expand_stack(struct vm_area_struct *vma, unsigned long address) +int expand_stack(struct vm_area_struct *vma, unsigned long address, + bool write_locked) { - return expand_downwards(vma, address); + if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) + return -EINVAL; + return expand_downwards(vma, address, write_locked); } -struct vm_area_struct * -find_extend_vma(struct mm_struct *mm, unsigned long addr) +struct vm_area_struct *find_extend_vma_locked(struct mm_struct *mm, + unsigned long addr, bool write_locked) { struct vm_area_struct *vma; unsigned long start; + int err; addr &= PAGE_MASK; vma = find_vma(mm, addr); @@ -2162,10 +2191,17 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr) return NULL; if (vma->vm_start <= addr) return vma; - if (!(vma->vm_flags & VM_GROWSDOWN)) - return NULL; start = vma->vm_start; - if (expand_stack(vma, addr)) + err = expand_stack(vma, addr, write_locked); + if (unlikely(err == -EAGAIN)) { + mmap_read_unlock(mm); + mmap_write_lock(mm); + vma = find_vma(mm, addr); + if (vma) + err = expand_stack(vma, addr, true); + mmap_write_downgrade(mm); + } + if (err) return NULL; if (vma->vm_flags & VM_LOCKED) populate_vma_page_range(vma, addr, start, NULL); @@ -2173,6 +2209,11 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr) } #endif +struct vm_area_struct *find_extend_vma(struct mm_struct *mm, + unsigned long addr) +{ + return find_extend_vma_locked(mm, addr, false); +} EXPORT_SYMBOL_GPL(find_extend_vma); /* diff --git a/mm/nommu.c b/mm/nommu.c index f670d9979a26..f4b4434c465f 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -643,7 +643,8 @@ struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr) * expand a stack to a given address * - not supported under NOMMU conditions */ -int expand_stack(struct vm_area_struct *vma, unsigned long address) +int expand_stack(struct vm_area_struct *vma, unsigned long address, + bool write_locked) { return -ENOMEM; }