From nobody Tue May 21 22:35:45 2024 X-Original-To: dev-commits-src-main@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4VkTmL0Wb0z5Kyj3; Tue, 21 May 2024 22:35:46 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4VkTmK6zchz4X6R; Tue, 21 May 2024 22:35:45 +0000 (UTC) (envelope-from git@FreeBSD.org) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1716330946; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=8uKxpXi9yYcN72yqVi0TYGHURbXdK7oyw6TMecd8RvI=; b=lTJlYh2anZ40ZQpZUU1CAawIFOBk+QPKDJa94+vQTzUqQ+fi7wAyXU+VBkvMF+PaNRUk+P NSmq2YhijyAkfdk9RX2Kmko1Qc2BakGX+eZkkPLYoT0P0IHYaz6AXBX94zmlBtnKkpfzgV k5DgrqfdUKOyGzOrR+F6fy3rpaudPXsjoTKikCTgwyb20l98uJq31iPx1Tgq+WQhGNloev VHwghmIOtXTEXqUwVFT7I20/7meDvaE/VJ2I5MzjLZGXT+xAM1yRwssem4U1SXDLm40240 wtdRStZ+ashTS7jUUlzooEtHhA5q9S5EOZHM91hgCZEcgeoGwI4G9F7/t1JcNw== ARC-Seal: i=1; s=dkim; d=freebsd.org; t=1716330946; a=rsa-sha256; cv=none; b=IV+1FP3n0y1IOvTz4uKU+eD8bQ47MILZgZzIJVqySnyLO8EY/LnuhxfCDeuoUkaYM2bzyS xX7SG8eOFRMY1w2SW759Vyb0LL2YUCTsXpPDEMFok017V2pjQwP9sqWVedfUvkPIvqf/+I SFuXQVbcmtZAQhyIg9olHnQFlax7Xr1CpzSelvgve9CqROyRokYsGelOJuEkM8/Ek4myWC bRCaHOE233EW5WjsIlCFLTtmshGy9/asY56q5HeRjlAfhdi7KD/L+DyhVj7w7R7wVTYMkX HdpR3s6zJcdPB5guVezZySX4zpM/cdg8p2j+CInUfsYC/3r4Mx2wMkLG04jjKg== ARC-Authentication-Results: i=1; mx1.freebsd.org; none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=freebsd.org; s=dkim; t=1716330946; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=8uKxpXi9yYcN72yqVi0TYGHURbXdK7oyw6TMecd8RvI=; b=yRQHhlvjtf1AQtfqYyFyR7BLoLcJuLwZQSxILkO2pUAWhGrYHbUjIOVkXbikzr4nSEhBm/ hXok+aFZ7VaZM3m8/Ch50aBrhHlPGFKVJliL9zx/uz1g7p7rz2exU093e2yHqjvTka3/5A IgSLseSRsiXkMrWXje6YvFSSaOPaKhiv2gBJjsnKgrINL5di59gRENj8/nqNCYFD6uJIqw 3wFiRSmNZyJCb4r+SNdktv1B4SBPpD12OzaxgtijfDqV7BLdjijBWy56VK95DQf+wtmU/g qf6eRO8TUQxu23SQ1z7N9KfoxzzA+JNFlUTh1kje2YFYyxtVhif6fzjHwrKFyg== Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 4VkTmK6b2TzggW; Tue, 21 May 2024 22:35:45 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.17.1/8.17.1) with ESMTP id 44LMZjn5095277; Tue, 21 May 2024 22:35:45 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.17.1/8.17.1/Submit) id 44LMZj3A095274; Tue, 21 May 2024 22:35:45 GMT (envelope-from git) Date: Tue, 21 May 2024 22:35:45 GMT Message-Id: <202405212235.44LMZj3A095274@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Dag-Erling =?utf-8?Q?Sm=C3=B8rgrav?= Subject: git: a4be1eb21165 - main - access(2): Discourage use of these system calls. List-Id: Commit messages for the main branch of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-main List-Help: List-Post: List-Subscribe: List-Unsubscribe: X-BeenThere: dev-commits-src-main@freebsd.org Sender: owner-dev-commits-src-main@FreeBSD.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: des X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: a4be1eb21165d7aedae9dc6634528619ff10d025 Auto-Submitted: auto-generated The branch main has been updated by des: URL: https://cgit.FreeBSD.org/src/commit/?id=a4be1eb21165d7aedae9dc6634528619ff10d025 commit a4be1eb21165d7aedae9dc6634528619ff10d025 Author: Dag-Erling Smørgrav AuthorDate: 2024-05-21 22:35:22 +0000 Commit: Dag-Erling Smørgrav CommitDate: 2024-05-21 22:35:22 +0000 access(2): Discourage use of these system calls. Fixes: 421025a274fb PR: 262895 MFC after: 3 days Reviewed by: emaste Differential Revision: https://reviews.freebsd.org/D45240 --- lib/libsys/access.2 | 105 +++++++++++++++++++++++++--------------------------- 1 file changed, 50 insertions(+), 55 deletions(-) diff --git a/lib/libsys/access.2 b/lib/libsys/access.2 index 91fe50a08cc4..46c00362a574 100644 --- a/lib/libsys/access.2 +++ b/lib/libsys/access.2 @@ -25,7 +25,7 @@ .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" -.Dd May 13, 2024 +.Dd May 21, 2024 .Dt ACCESS 2 .Os .Sh NAME @@ -45,35 +45,43 @@ .Fn faccessat "int fd" "const char *path" "int mode" "int flag" .Sh DESCRIPTION The -.Fn access -and +.Fn access , .Fn eaccess -system calls check the accessibility of the -file named by -the +and +.Fn faccessat +system calls report whether an attempt to access the file designated +by their .Fa path -argument -for the access permissions indicated by -the +in the manner described by their .Fa mode -argument. +argument is likely to succeed. The value of .Fa mode -is either the bitwise-inclusive OR of the access permissions to be -checked -.Dv ( R_OK +is either the bitwise-inclusive OR of the desired permissions +.Po +.Dv R_OK for read permission, .Dv W_OK for write permission, and .Dv X_OK -for execute/search permission), -or the existence test -.Pq Dv F_OK . +for execute / search permission +.Pc +or +.Dv F_OK +to simply check whether the file exists. .Pp -For additional information, see the -.Sx "File Access Permission" -section of -.Xr intro 2 . +For a number of reasons, these system calls cannot be relied upon to +give a correct and definitive answer. +They can at best provide an early indication of the expected outcome, +to be confirmed by actually attempting the operation. +For existence checks, either +.Xr stat 2 +or +.Xr lstat 2 +should be used instead. +See also +.Sx SECURITY CONSIDERATIONS +below. .Pp The .Fn eaccess @@ -87,6 +95,13 @@ the real user ID in place of the effective user ID, the real group ID in place of the effective group ID, and the rest of the group access list. .Pp +See the +.Sx DEFINITIONS +section of +.Xr intro 2 +for additional information on file access permissions and real +vs. effective user and group IDs. +.Pp The .Fn faccessat system call is equivalent to @@ -114,8 +129,10 @@ list, defined in .In fcntl.h : .Bl -tag -width indent .It Dv AT_EACCESS -The checks for accessibility are performed using the effective user and group -IDs instead of the real user and group ID as required in a call to +The checks are performed using the effective user and group IDs, +like +.Fn eaccess , +instead of the real user and group ID, like .Fn access . .It Dv AT_RESOLVE_BENEATH Only walk paths below the directory specified by the @@ -147,23 +164,15 @@ Likewise for .Dv R_OK and .Dv W_OK . -.Pp -.Fn access , -.Fn eaccess -and -.Fn faccessat -will always dereference symbolic links. -If the symbolic link itself needs to be referenced, -.Xr lstat 2 -should be used instead. .Sh RETURN VALUES .Rv -std .Sh ERRORS +The .Fn access , .Fn eaccess , -or +and .Fn faccessat -will fail if: +system calls may fail if: .Bl -tag -width Er .It Bq Er EINVAL The value of the @@ -254,25 +263,11 @@ system call appeared in .Fx 8.0 . .Sh SECURITY CONSIDERATIONS The -.Fn access -system call -is a potential security hole due to race conditions and -should never be used. -Set-user-ID and set-group-ID applications should restore the -effective user or group ID, -and perform actions directly rather than use -.Fn access -to simulate access checks for the real user or group ID. -The -.Fn eaccess -system call -likewise may be subject to races if used inappropriately. -.Pp -.Fn access -remains useful for providing clues to users as to whether operations -make sense for particular filesystem objects (e.g. 'delete' menu -item only highlighted in a writable folder ... avoiding interpretation -of the st_mode bits that the application might not understand -- -e.g. in the case of AFS). -It also allows a cheaper file existence test than -.Xr stat 2 . +.Fn access , +.Fn eaccess , +and +.Fn faccessat +system calls are subject to time-of-check-to-time-of-use races and +should not be relied upon for file permission enforcement purposes. +Instead, applications should perform the desired action using the +requesting user's credentials.