CVE-2025-38614 (GCVE-0-2025-38614)

Vulnerability from cvelistv5 – Published: 2025-08-19 17:03 – Updated: 2025-11-03 17:40
VLAI?
Title
eventpoll: Fix semi-unbounded recursion
Summary
In the Linux kernel, the following vulnerability has been resolved: eventpoll: Fix semi-unbounded recursion Ensure that epoll instances can never form a graph deeper than EP_MAX_NESTS+1 links. Currently, ep_loop_check_proc() ensures that the graph is loop-free and does some recursion depth checks, but those recursion depth checks don't limit the depth of the resulting tree for two reasons: - They don't look upwards in the tree. - If there are multiple downwards paths of different lengths, only one of the paths is actually considered for the depth check since commit 28d82dc1c4ed ("epoll: limit paths"). Essentially, the current recursion depth check in ep_loop_check_proc() just serves to prevent it from recursing too deeply while checking for loops. A more thorough check is done in reverse_path_check() after the new graph edge has already been created; this checks, among other things, that no paths going upwards from any non-epoll file with a length of more than 5 edges exist. However, this check does not apply to non-epoll files. As a result, it is possible to recurse to a depth of at least roughly 500, tested on v6.15. (I am unsure if deeper recursion is possible; and this may have changed with commit 8c44dac8add7 ("eventpoll: Fix priority inversion problem").) To fix it: 1. In ep_loop_check_proc(), note the subtree depth of each visited node, and use subtree depths for the total depth calculation even when a subtree has already been visited. 2. Add ep_get_upwards_depth_proc() for similarly determining the maximum depth of an upwards walk. 3. In ep_loop_check(), use these values to limit the total path length between epoll nodes to EP_MAX_NESTS edges.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < 71379495ab70eaba19224bd71b5b9b399eb85e04 (git)
Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < 1b13b033062824495554e836a1ff5f85ccf6b039 (git)
Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < 2a0c0c974bea9619c6f41794775ae4b97530e0e6 (git)
Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < 7a2125962c42d5336ca0495a9ce4cb38a63e9161 (git)
Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < ea5f97dbdcb1651581a22bd10afd2f0dd9dc11d6 (git)
Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < 3542c90797bc3ab83ebab54b737d751cf3682036 (git)
Affected: 22bacca48a1755f79b7e0f192ddb9fbb7fc6e64e , < f2e467a48287c868818085aa35389a224d226732 (git)
Affected: 8216e1a0d47cae06a75c42346f19dffe14e42d57 (git)
Affected: 28a92748aa4bc57d35e7b079498b0ac2e7610a37 (git)
Affected: 7eebcd4792c5a341559aed327b6afecbb1c46402 (git)
Affected: 0eccd188cfeaf857a26f2d72941d27d298cf6a54 (git)
Affected: a72affdbb09f3f24f64ffcbbdf62c2e57c58f379 (git)
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    Linux Linux Affected: 2.6.38
Unaffected: 0 , < 2.6.38 (semver)
Unaffected: 5.15.190 , ≤ 5.15.* (semver)
Unaffected: 6.1.149 , ≤ 6.1.* (semver)
Unaffected: 6.6.103 , ≤ 6.6.* (semver)
Unaffected: 6.12.43 , ≤ 6.12.* (semver)
Unaffected: 6.15.11 , ≤ 6.15.* (semver)
Unaffected: 6.16.1 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\neventpoll: Fix semi-unbounded recursion\n\nEnsure that epoll instances can never form a graph deeper than\nEP_MAX_NESTS+1 links.\n\nCurrently, ep_loop_check_proc() ensures that the graph is loop-free and\ndoes some recursion depth checks, but those recursion depth checks don\u0027t\nlimit the depth of the resulting tree for two reasons:\n\n - They don\u0027t look upwards in the tree.\n - If there are multiple downwards paths of different lengths, only one of\n   the paths is actually considered for the depth check since commit\n   28d82dc1c4ed (\"epoll: limit paths\").\n\nEssentially, the current recursion depth check in ep_loop_check_proc() just\nserves to prevent it from recursing too deeply while checking for loops.\n\nA more thorough check is done in reverse_path_check() after the new graph\nedge has already been created; this checks, among other things, that no\npaths going upwards from any non-epoll file with a length of more than 5\nedges exist. However, this check does not apply to non-epoll files.\n\nAs a result, it is possible to recurse to a depth of at least roughly 500,\ntested on v6.15. (I am unsure if deeper recursion is possible; and this may\nhave changed with commit 8c44dac8add7 (\"eventpoll: Fix priority inversion\nproblem\").)\n\nTo fix it:\n\n1. In ep_loop_check_proc(), note the subtree depth of each visited node,\nand use subtree depths for the total depth calculation even when a subtree\nhas already been visited.\n2. Add ep_get_upwards_depth_proc() for similarly determining the maximum\ndepth of an upwards walk.\n3. In ep_loop_check(), use these values to limit the total path length\nbetween epoll nodes to EP_MAX_NESTS edges."
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          "url": "https://git.kernel.org/stable/c/f2e467a48287c868818085aa35389a224d226732"
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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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