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Mon, 29 Apr 2024 22:36:49 -0700 (PDT) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id n1-20020a170902d2c100b001e2a7e90321sm21334480plc.224.2024.04.29.22.36.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Apr 2024 22:36:48 -0700 (PDT) Date: Mon, 29 Apr 2024 22:36:48 -0700 From: Kees Cook To: Allen Cc: Allen Pais , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, ebiederm@xmission.com, mcgrof@kernel.org, j.granados@samsung.com Subject: Re: [RFC PATCH] fs/coredump: Enable dynamic configuration of max file note size Message-ID: <202404292236.568F42D3C@keescook> References: <20240429172128.4246-1-apais@linux.microsoft.com> <202404291245.18281A6D@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: wtsnk15969afzar198jmphk3efrd6x9z X-Rspam-User: X-Rspamd-Queue-Id: A3B4E100008 X-Rspamd-Server: rspam05 X-HE-Tag: 1714455410-812087 X-HE-Meta: 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 D6/buKj6 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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 Mon, Apr 29, 2024 at 03:35:01PM -0700, Allen wrote: > On Mon, Apr 29, 2024 at 12:49 PM Kees Cook wrote: > > > > On Mon, Apr 29, 2024 at 05:21:28PM +0000, Allen Pais wrote: > > > Introduce the capability to dynamically configure the maximum file > > > note size for ELF core dumps via sysctl. This enhancement removes > > > the previous static limit of 4MB, allowing system administrators to > > > adjust the size based on system-specific requirements or constraints. > > > > Under what conditions is this actually needed? > > I addressed this in the email I sent out before this. > > > > > > [...] > > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > > > index 81cc974913bb..80cdc37f2fa2 100644 > > > --- a/kernel/sysctl.c > > > +++ b/kernel/sysctl.c > > > @@ -63,6 +63,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > #include "../lib/kstrtox.h" > > > > > > @@ -1623,6 +1624,13 @@ static struct ctl_table kern_table[] = { > > > .mode = 0644, > > > .proc_handler = proc_dointvec, > > > }, > > > + { > > > + .procname = "max_file_note_size", > > > + .data = &max_file_note_size, > > > + .maxlen = sizeof(unsigned int), > > > + .mode = 0644, > > > + .proc_handler = proc_dointvec, > > > + }, > > > > Please don't add new sysctls to kernel/sysctl.c. Put this in fs/coredump.c > > instead, and name it "core_file_note_size_max". (A "max" suffix is more > > common than prefixes, and I'd like it clarified that it relates to the > > coredumper with the "core" prefix that match the other coredump sysctls. > > > > -Kees > > Makes sense. Let me know if the below looks fine, > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 5397b552fbeb..6aebd062b92b 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1564,7 +1564,6 @@ static void fill_siginfo_note(struct memelfnote > *note, user_siginfo_t *csigdata, > fill_note(note, "CORE", NT_SIGINFO, sizeof(*csigdata), csigdata); > } > > -#define MAX_FILE_NOTE_SIZE (4*1024*1024) > /* > * Format of NT_FILE note: > * > @@ -1592,7 +1591,7 @@ static int fill_files_note(struct memelfnote > *note, struct coredump_params *cprm > > names_ofs = (2 + 3 * count) * sizeof(data[0]); > alloc: > - if (size >= MAX_FILE_NOTE_SIZE) /* paranoia check */ > + if (size >= core_file_note_size_max) /* paranoia check */ > return -EINVAL; > size = round_up(size, PAGE_SIZE); > /* > diff --git a/fs/coredump.c b/fs/coredump.c > index be6403b4b14b..2108eb93acb9 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -56,10 +56,13 @@ > static bool dump_vma_snapshot(struct coredump_params *cprm); > static void free_vma_snapshot(struct coredump_params *cprm); > > +#define MAX_FILE_NOTE_SIZE (4*1024*1024) > + > static int core_uses_pid; > static unsigned int core_pipe_limit; > static char core_pattern[CORENAME_MAX_SIZE] = "core"; > static int core_name_size = CORENAME_MAX_SIZE; > +unsigned int core_file_note_size_max = MAX_FILE_NOTE_SIZE; > > struct core_name { > char *corename; > @@ -1020,6 +1023,13 @@ static struct ctl_table coredump_sysctls[] = { > .mode = 0644, > .proc_handler = proc_dointvec, > }, > + { > + .procname = "core_file_note_size_max", > + .data = &core_file_note_size_max, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_douintvec, > + }, > }; > > static int __init init_fs_coredump_sysctls(void) > diff --git a/include/linux/coredump.h b/include/linux/coredump.h > index d3eba4360150..14c057643e7f 100644 > --- a/include/linux/coredump.h > +++ b/include/linux/coredump.h > @@ -46,6 +46,7 @@ static inline void do_coredump(const > kernel_siginfo_t *siginfo) {} > #endif > > #if defined(CONFIG_COREDUMP) && defined(CONFIG_SYSCTL) > +extern unsigned int core_file_note_size_max; > extern void validate_coredump_safety(void); > #else > static inline void validate_coredump_safety(void) {} Yes; thank you! I like this naming (and sysctl location) now. :) -Kees -- Kees Cook