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U2FsdGVkX1/Sjq2h8MMf9oWv52tFvhUBGDANuZ3LdPoUbZMRUp3XDUr867l/97Wdzl1+VyiZKrPFshkIwK2U8cp8wysRWRi7R7mqiRGSNAHs+eJ6jchvFSG85Tmz5vCOAN9LgxA3uEE3+rfhH9v599FPLCanKzGBrCflrdLALiTj0pQpjhXMohyOgKIqSbuGq0yyQmJdALha05vyKaJL5Kic7vQSOlrMP6TB9v5PbKnaYkST9XNLD93WnxEC+u5Ou5stpZUlYNJbDTh87p2YCgUzTzlYWipFpYWwxc9V5mk82RDMEJgNhtyhScCtrjgsQANr7xtPJRNEef44N2tGCOkq+2f8TiYI8//zoK43JlXmw9eFJMuC+Phwp9qCaaORHaGUgqrlpjR0H3aI53jcCzKzhhIY+G1OoI68wdJlXYnLvf9xRj8fetCCOm0Z07PvqvO0rfHQ8aS20cg1HmIebraYY7z9PJlaYD5VLsHxd3nzNCuchTDVi2RXdcD+s/Zn2mUkUcD++8tfZko3IiN0nNo7KSTxNf0fR/XTbCv3KBEhPMUmxIvyENFIOYd7b9mKg7OVcgC/TXczfQPZcy5Ku5Jf47pgn6oXstR1bogP8sQZH37wLcqIADePZtkzBWPG40zMGtxstwOMmPACxcrbABpZTcwu08kM9vHzknsERmb3i2ywzIFC/LjchMeGeuAS9FkFzsNzrGUoStu4MuczTps71TOIpxsmIY+afjs2Qo0gPjEmSL5dEjDDt4O7j0rIRmPMKMwpO3eVpaOetedLfLN57nsSPM3r6I/1GGPL8gR1KJw74lQ4JYnB+Fc4aTQZ0sDyW/XtDVdIyXoykklz8qpTmgpLfPpj2Lnp4Tq1/Xk6gSkx+5Q98SJg1v+bDNGj00jnKRbYse3AiTz/6xKVQCAvWsJKj+bIw6hxGoL6Y+kg3i0+V/XExOSPgEW+3koVjf/HUNZqguo+/g0wUlT txDv4gX9 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 21, 2025 at 01:40:56PM -0700, Kees Cook wrote: > Hi! > > This is very much an RFC series, but I wanted to make sure it actually > worked before I proposed it. This series seeks to give kfree() the >` side-effect of assigning NULL to the kfree() argument when possible. > This would make a subset of "dangling pointer" flaws turn into NULL > derefs instead of Use-After-Free[1]. It effectively turns: > > kfree(var); > > into: > > kfree(var); > var = NULL; > > when "var" is actually addressable. (i.e. not "kfree(get_ptrs())" etc.) Maybe a dumb question, but if 'var' is a local variable, is it common that a dangling pointer in a local variable to lead to a use-after-free bug? Also, I don't expect this to have a significant performance impact, but have you measured it and is the overhead low enough to enable it unconditionally? > It depends on a builtin, __builtin_is_lvalue(), which is not landed in any > compiler yet, but I do have it working in a Clang patch[2]. This should > be essentially free (pardon the pun), so I think if folks can tolerate > a little bit of renaming needed for when kfree is needed as a function > and not a macro, it should be good. Please let me know what you think. I don't have a strong opinion on the slab side, but now users of kfree should be aware of this subtle change (e.g., when debugging code). -- Cheers, Harry (formerly known as Hyeonggon) > Thanks! > > -Kees > > (Yes, I'm still working on the kmalloc_objs() series, but I needed to > take a break from fixing all the allocation corner cases I've found there.) > > [1] https://github.com/KSPP/linux/issues/87 > [2] https://github.com/kees/llvm-project/commits/builtin_is_lvalue/ > > Kees Cook (5): > treewide: Replace kfree() casts with union members > treewide: Prepare for kfree() to __kfree() rename > compiler_types: Introduce __is_lvalue() > slab: Set freed variables to NULL by default > [DEBUG] slab: Report number of NULLings > > arch/mips/alchemy/common/dbdma.c | 2 +- > include/linux/compiler_types.h | 10 ++++++++++ > include/linux/netlink.h | 1 + > include/linux/slab.h | 33 ++++++++++++++++++++++++++++++-- > include/net/pkt_cls.h | 5 ++++- > io_uring/futex.c | 2 +- > io_uring/io_uring.c | 12 ++++++------ > kernel/bpf/core.c | 3 ++- > mm/slab_common.c | 12 ++++++++---- > mm/slub.c | 6 +++--- > net/sched/ematch.c | 2 +- > net/wireless/nl80211.c | 2 +- > 12 files changed, 69 insertions(+), 21 deletions(-) > > -- > 2.34.1 >